Optical display

ABSTRACT

An optical display provided with a hologram element and a light source, wherein the hologram is a reflection hologram formed by a light beam which is obtained by utilizing light passing through a slit and has information on an object and a reference light beam which has an incident ligth path different from that of the light having the information on an object, and the reproduced image of the object is displayed using the light from the light source.

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCTINTERNATIONAL APPLICATION PCT/JP98/0114

TECHNICAL FIELD

The present invention relates to an optical display apparatus fordisplaying image information and character information.

BACKGROUND ART

In recent years, an optical display apparatus for displaying imageinformation and character information has been used in various fields.An example of such an optical display apparatus is an electronic opticaldisplay apparatus widely used in a traffic information display board, adirection board or a billboard. Related techniques are disclosed in, forexample, Japanese Laid-Open Publication Nos. 6-228921, 7-129108,7-140912, 8-6513, 8-158322, 8-160894, etc. First, one of the mosttypical examples of such an optical display apparatus, an opticaltraffic sign incorporating a fluorescent lamp therein, will be describedbelow with reference to the figures. However, various other conventionalstructures are known in the art, such as those incorporating an LED oran EL device for producing a self-luminous display, and those using anoptical fiber or a light guide plate for guiding light from a lightsource.

FIG. 1A is a side view illustrating a structure of a conventionaloptical traffic sign, and FIG. 1B is a front view illustrating the same.Specifically, reference numeral 156 denotes a sign display board, 157 aring-shaped fluorescent tube, 158 a sign body, and 159 a sign pole.

The sign display board 156 includes a semi-transparent resin on which asign pattern is printed. The sign can be recognized even at night byilluminating the pattern from the inside of the sign with light from thering-shaped fluorescent tube 157. The sign body 158, supporting thering-shaped fluorescent tube 157 and the sign display board 156, isinstalled on a side wall beside a road or on a tunnel ceiling by beingsupported by the sign pole 159.

However, the above-described conventional structure has the followingproblems.

First, since the sign pattern is either printed on the semi-transparentresin or is made of a color resin, a large portion of light emitted bythe ring-shaped fluorescent tube 157, as a light source, is absorbed bythe resin, whereby the display is not sufficiently bright.

Second, since the display section, including the sign display board 156and the fluorescent tube (light source) 157, is supported by the signbody 158, the portion including the display section is large and heavy.Moreover, since the sign pole 159 supporting the same must also berobust, the overall structure is even larger and heavier.

Third, the structure must be installed so that it substantially projectsfrom the installation surface, i.e., a road side wall or a tunnelceiling. Therefore, it may be hit for some reasons by a moving objectsuch as a person, a car or a load, thereby damaging the displayapparatus body while also damaging the moving object. To avoid such anaccident requires a large installation space, which is not economical.

The above-described problems arise not only from the optical trafficsign incorporating a fluorescent lamp therein, illustrated in FIGS. 1Aand 1B as a conventional example, but also from those of a self-luminoustype such as an LED or those using an optical fiber or a light guideplate for guiding light from the light source. Moreover, the problemsare not limited to the above-described traffic sign, but are common to ageneral class of optical display apparatuses where a pattern to bedisplayed is illuminated with light from a light source.

Those using a hologram are possible alternatives which may solve theabove-described problems.

First, a principle of producing a hologram based on a commonly-employedconventional technique and a principle of displaying (reconstructing)image information using such a conventional hologram will be describedbelow.

FIG. 2A is a diagram schematically illustrating a typically-employedprinciple of producing a hologram.

In particular, an object O is illuminated with object illumination lightIL emitted from a laser light source, thereby forming object light OLhaving information relating to the shape, etc., of the object O, andmaking the object light OL be incident upon a hologram dry plate H1. Atthe same time, reference light RL1, formed by splitting light emittedfrom the same laser light source as the object illumination light IL bymeans of a beam splitter, or the like, is directed to be incident uponthe hologram dry plate H1 from an inclined direction. Thus, interferencefringes between the object light OL and the reference light RL1 arerecorded on the hologram dry plate H1. The hologram dry plate H1 onwhich such interference fringes (having information of the object O) arerecorded will hereinafter be referred to also as the “hologram plateH1”.

FIG. 2B is a diagram schematically illustrating a principle ofreconstructing the hologram plate H1 which is provided according to FIG.2A.

In particular, the reconstruction illumination light RI1, which is lightfrom the same laser light source as that used for producing the hologramplate H1, is directed to propagate through the same path as that for thereference light RL1 (see FIG. 2A) so as to irradiate the hologram plateH1. Thus, light (reconstruction light) R1, having information of theobject recorded on the hologram plate H1, is reconstructed, so that areconstructed image I1 is observed at a position where the object wasoriginally located.

The above-described method, however, requires the use of a laser lightsource as a light source when producing and reconstructing the hologramplate H1, and thus has such problems that the cost cannot be reduced andthe handling thereof is complicated.

On the other hand, in a reflection-type hologram to be described below,a hologram image can be reconstructed using white light.

To produce a reflection-type hologram, the hologram plate H1 is firstproduced by the method as illustrated in FIG. 2A, and then irradiatedwith reconstruction illumination light (laser light) RI21, asillustrated in FIG. 3A, in a direction opposite to that of thereconstruction illumination light RI1 illustrated in FIG. 2B. Thus,reconstruction light R21, directed from the hologram plate H1 to theposition where the object was located, is reconstructed, therebyreconstructing a real image (reconstructed image) I21 of the object at aposition where the object was located. Then, a new hologram dry plate H2is placed at a position spaced apart from the reconstructed image I21 ofthe object by a distance Z0, as illustrated in FIG. 3B, and referencelight RL2 is directed to be incident upon the hologram dry plate H2 froman inclined direction opposite from the hologram plate H1. The referencelight RL2 is formed by splitting light emitted from the same laser lightsource as the reconstruction illumination light RI21 by means of a beamsplitter, or the like. Thus, interference fringes between thereconstruction illumination light RI21 and the reference light RL2 arerecorded on the hologram dry plate H2. The hologram dry plate H2 onwhich such interference fringes (having information of the object) arerecorded as a reflection-type hologram will hereinafter be referred toalso as the “reflection-type hologram plate H2”.

FIG. 3C is a diagram schematically illustrating a principle ofreconstructing the reflection-type hologram plate H2 formed as describedabove.

In particular, the reflection-type hologram plate H2 is irradiated withreconstruction illumination light RI22 (white light from a point lightsource spaced apart from the reflection-type hologram plate H2 by acertain distance) which propagates in a direction diametrically oppositeto that of the reference light RL2 illustrated in FIG. 3B. Thus,reconstruction light R22 having information of the object recorded onthe reflection-type hologram plate H2 is reconstructed so as to form areconstructed image I22 at a position where the object was originallylocated.

In a reflection-type hologram, a wavelength selectivity (colorselectivity) in the optical diffraction characteristic (the diffractionefficiency) is high. Therefore, the image I22 is reconstructed by lighthaving a wavelength close to that of the laser light used for producingthe hologram. Thus, a color image can also be reconstructed bysuperposition. However, a clear reconstructed image cannot be obtainedwhen the distance z0 between the position of the reflection-typehologram plate H2 and a position where the reconstructed image I22 isdisplayed is large.

The reason why a reconstructed image of the reflection-type hologram isblurred will further be described with reference to FIGS. 3D and 3E.

The reconstruction illumination light RI22 directed toward thereflection-type hologram is white light. Therefore, wavelengths otherthan a wavelength λ0 of the laser light used to produce the hologram arealso contained in the reconstruction illumination light RI22. Areflection-type hologram has a high wavelength selectivity, as shown ina graph of FIG. 3B illustrating the wavelength dependency of thediffraction efficiency, whereby substantially none of light having awavelength far away from the wavelength (center wavelength) λ0 of thelaser light used to produce the hologram is diffracted. Therefore, onlylight having a wavelength close to the center wavelength λ0 isdiffracted, thereby reconstructing the image I22. In practice, however,light having a wavelength which is close to, but different from, thecenter wavelength λ0, as represented by λ1 and λ2 in FIGS. 3D and 3E, isalso contained in the reconstructed light R22, thereby also forming andsuperimposing reconstructed images from such light on the intendedreconstructed image from the light having the center wavelength λ0. Bythis effect, the reconstructed image I22 is blurred when the distance z0to the position where the image I22 is formed is set to be large. Thatis, with a reflection-type hologram, a clear reconstructed image I22cannot be viewed when it is viewed from a distance greater than thedistance z0 set when producing the hologram. This can be a very criticaldisadvantage in an application, such as an optical informationapparatus, e.g., a traffic sign, which aims to clearly transferprescribed information.

As described above, the commonly-employed conventional hologram and thereflection-type hologram using the same have significant problems to besolved, in terms of the cost, the accurate display/transfer ofinformation, etc., before they can be used in an optical displayapparatus such as a traffic sign, for example.

A hologram display method different from those described above is whatis known as a rainbow hologram.

To produce a rainbow hologram, the hologram plate H1 is first producedby the method as illustrated in FIG. 2A, which is then irradiated withreconstruction illumination light (laser light) RI31 in a directionopposite to that of the reconstruction illumination light RI1illustrated in FIG. 2B and through a slit having a width of Δ, asillustrated in FIG. 4A. Thus, reconstruction light R31, directed fromthe hologram plate H1 to the position where the object was located, isreconstructed, thereby reconstructing a real image (reconstructed image)I31 of the object at a position where the object was located. Then, anew hologram dry plate H3 is placed at a position spaced apart from thereconstructed image I31 of the object by a distance Z0, as illustratedin FIG. 4B, and reference light RL3 is directed to be incident upon thehologram dry plate H3 from an inclined direction as that for thehologram plate H1. The reference light RL3 is formed by splitting lightemitted from the same laser light source as the reconstructionillumination light RI31 by means of a beam splitter, or the like. Thus,interference fringes between the reconstruction illumination light RI31and the reference light RL3 are recorded on the hologram dry plate H3.The hologram dry plate on which such interference fringes (havinginformation of the object) are recorded as a transmission-type hologramby the rainbow hologram method will hereinafter be referred to also asthe “rainbow hologram plate H3”.

FIG. 4C is a diagram schematically illustrating a principle ofreconstructing the rainbow hologram plate H3 formed as described above.

In particular, the rainbow hologram plate H3 is irradiated withreconstruction illumination light RI32 (white light from a point lightsource spaced apart from the rainbow hologram plate H3 by a certaindistance) which propagates in a direction diametrically opposite to thatof the reference light RL3 illustrated in FIG. 4B. Thus, reconstructionlight R32 having information of the object recorded on the rainbowhologram plate H3 is reconstructed and directed toward the positionwhere the slit was located during the hologram production, so as to forma reconstructed image I32 at a position where the object was originallylocated.

With a rainbow hologram formed as described above, a clearerreconstructed image is observed as compared to that observed by areflection-type hologram. The reason for this will be described withreference to FIGS. 4D and 4E.

The reconstruction illumination light RI32 directed toward the rainbowhologram is white light. Therefore, wavelengths other than a wavelengthλ0 of the laser light used to produce the hologram are also contained inthe reconstruction illumination light RI32. However, a rainbow hologram,which is a transmission-type hologram, has a low wavelength selectivity,as shown in a graph of FIG. 4E illustrating the wavelength dependency ofthe diffraction efficiency, whereby a relatively wide range ofwavelengths are diffracted to emit the reconstruction light R32, therebyreconstructing the images I32 respectively corresponding to differentwavelengths of light. However, since a slit is used when producing therainbow hologram, the reconstructed images formed by the differentwavelengths of light are formed at respectively different positions(i.e., spatially separated from one another). For example, reconstructedimages formed by light having wavelengths which are different from thecenter wavelength λ0, as represented by λ1 and λ2 in FIGS. 4D and 4E,are formed concurrently at positions different from that of thereconstructed image formed by light having the center wavelength λ0, butare not spatially superimposed on the intended reconstructed imageformed by the light having the center wavelength λ0. Therefore, with therainbow hologram, the reconstructed image I32 is relatively clearlyobserved, with the color of the image I32 changing as the observationposition changes.

The phenomenon that the reconstructed image I32 is observed withdifferent colors depending upon the observation position is where thenomenclature “rainbow hologram” comes from, and various applicationshave been proposed in the art which take advantage of the phenomenon.However, in view of reconstructing a color image, on the other hand,such a change in the color of the reconstructed image I32 depending uponthe observation position presents a disadvantage that a prescribed colorimage cannot be reconstructed. For example, in the case of the trafficsign as described above, use of a predetermined color also constitutes apart of the information to be transferred. Therefore, theabove-described characteristic of the rainbow hologram presents a verycritical disadvantage in the application thereof to an opticalinformation apparatus aims to clearly transfer prescribed information.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above-describedproblems existing in the prior art, and has an objective of providing alight-weight optical display apparatus which occupies a small space andis capable of reconstructing/displaying image information in a brightand clear manner, by using a hologram technique based on a novel method.

An optical display apparatus provided by one aspect of the presentinvention includes a hologram device and a light source. The hologram isa reflection-type hologram formed by: light having information of anobject which is obtained by using light having passed through a slit;and reference light having an incident optical path different from thatof the light having the information of the object, wherein areconstructed image of the object is displayed by light from the lightsource. The above-described object is accomplished by such a feature.

In one embodiment, the light having the information of the object isobject light which is obtained by irradiating the object with diffusedlight having passed through the slit. The diffused light may be formedby passing light through a ground glass.

In another embodiment, the light having the information of the object isreconstructed light obtained by reconstructing a transmission-typehologram which is formed by: object light obtained by irradiating theobject with diffused light having passed through the slit; andirradiation light having an incident optical path different from that ofthe object light. The diffused light may be formed by passing lightthrough a ground glass.

In still another embodiment, the light having the information of theobject is reconstructed light of a transmission-type hologram which isobtained by passing through the slit which is arranged to be adjacent tothe transmission-type hologram on which an image of the object isrecorded.

In still another embodiment, the light having the information of theobject is reconstructed light of a transmission-type hologram which isobtained by passing through: the slit which is arranged to be adjacentto the transmission-type hologram on which an image of the object isrecorded; and a cylindrical lens having its generatrix along alongitudinal direction of the slit.

The reference light is provided by superposing a plurality of beams onone another in a direction orthogonal to a longitudinal direction of theslit.

Preferably, the light source is a linear light source. The linear lightsource may be arranged on or in a vicinity of a plane orthogonal to alongitudinal direction of the slit.

In one embodiment, an incident plane of the reference light is a planeorthogonal to a longitudinal direction of the slit. Alternatively, anincident plane of the reference light may be a plane different from aplane orthogonal to a longitudinal direction of the slit.

An optical display apparatus provided by another aspect of the presentinvention is an optical display apparatus including a hologram deviceand a light source. The hologram is a reflection-type hologram formedby: light having information of an object which is obtained by usingdiffused light diffusing in one direction; and reference light having anincident optical path different from that of the light having theinformation of the object, wherein a reconstructed image of the objectis displayed by light from the light source. The above-described objectis accomplished by such a feature.

In one embodiment, the light having the information of the object isobject light which is obtained by irradiating the object with thediffused light.

In another embodiment, the light having the information of the object isreconstructed light obtained by reconstructing a transmission-typehologram which is formed by: object light obtained by irradiating theobject with the diffused light; and irradiation light having an incidentoptical path different from that of the object light. The referencelight may be provided by superposing a plurality of beams on one anotherin a direction orthogonal to the direction in which the diffused lightdiffuses.

In still another embodiment, the light having the information of theobject is reconstructed light of a transmission-type hologram which isobtained by passing through the slit which is arranged to be adjacent tothe transmission-type hologram on which an image of the object isrecorded. The reference light may be provided by superposing a pluralityof beams on one another in a direction orthogonal to the direction inwhich the diffused light diffuses.

In one embodiment, the diffused light is formed by passing light througha lenticular lens.

Preferably, the light source is a linear light source. The linear lightsource may be arranged on or in a vicinity of a plane orthogonal to thedirection in which the diffused light diffuses.

In one embodiment, an incident plane of the reference light is a planeorthogonal to the direction in which the diffused light diffuses.Alternatively, an incident plane of the reference light may be a planedifferent from a plane orthogonal to the direction in which the diffusedlight diffuses.

According to the present invention, there is provided an optical displaysystem having a plurality of display units arranged on an arrangementplane in which reconstructed images from the plurality of units aresynthesized and displayed, wherein each of the plurality of units is anoptical display apparatus of the present invention having theabove-described feature.

The hologram device in the optical display apparatus of the presentinvention may be provided by combining a plurality of hologram elementswith one another.

The hologram device in the optical display apparatus of the presentinvention may be formed on a flexible substrate.

The hologram device in the optical display apparatus of the presentinvention may be portable.

The light source in the optical display apparatus of the presentinvention may be a linear light source; and a length and an installationdirection of the linear light source may be set so that a predeterminedreconstructed image viewing range is obtained.

The light source in the optical display apparatus of the presentinvention may be a linear light source; and a position where areconstructed image is formed may be shifted by moving the linear lightsource out of an incident plane.

In some cases, the optical display apparatus of the present inventionincludes a plurality of the hologram devices, wherein the plurality ofhologram devices are reconstructed by one light source.

The light source in the optical display apparatus of the presentinvention may be a linear light source. In some cases, the linear lightsource is a fluorescent lamp or a combination of a fluorescent lamp anda reflecting plate.

The light source in the optical display apparatus of the presentinvention may be a linear light source including a polygon mirror and apoint light source.

The light source in the optical display apparatus of the presentinvention may be a linear light source which is a linear light sourcecomprising a cylindrical mirror and a point light source.

The light source in the optical display apparatus of the presentinvention may be a linear light source configured by a light beam whichis linearly focused by a mirror or a lens.

The light source in the optical display apparatus of the presentinvention may be a linear light source including an array of point lightsources.

The light source in the optical display apparatus of the presentinvention may be a linear light source configured by a bright linedisplayed on a two-dimensional display apparatus.

According to the present invention, there may be provided an opticaldisplay system, including an optical display apparatus of the presentinvention having the above-described feature and an informationcommunication apparatus. The optical display apparatus maythree-dimensionally display a communication area of the informationcommunication apparatus. A display area of the optical display apparatusand the communication area of the information communication apparatusmay match with each other. The information communication apparatus mayperform a one-way communication or an interactive communication ofinformation.

An optical display apparatus provided by another aspect of the presentinvention includes an image display apparatus, an imaging optical systemand a hologram screen. The hologram screen is arranged to reflect lightfrom a point light source so as to form a point image at a positiondifferent from the point light source; and the imaging optical system isarranged to adjust a focus in a vertical direction of an image displayedon the image display apparatus to coincide with the hologram screen. Theabove-described object is accomplished by such a feature.

In one embodiment, the formed point image is a real image.

In another embodiment, the formed point image is a false image formed ata position on an opposite side of the point light source with respect tothe hologram screen.

In one embodiment, the imaging optical system has independent imagingfunctions in a vertical direction and in a lateral direction. For thevertical direction, a focus in the vertical direction of an imagedisplayed on the image display apparatus is adjusted to coincide withthe hologram screen; and for the lateral direction, a focal distance isarranged to be variable.

The above-described optical display apparatus may further includepolarization glasses whose polarization transmission directions forrespective eyes are orthogonal to each other.

According to the present invention, there may be provided an opticaldisplay system having a plurality of display units arranged in a lateraldirection, wherein each of the plurality of display units is the opticaldisplay apparatus of the present invention having the above-describedfeature.

Moreover, according to the present invention, there may be provided anoptical display system having a plurality of display units arranged in adepth direction, wherein each of the plurality of display units is theoptical display apparatus of the present invention having theabove-described feature.

The image display apparatus may include: a display device selected froman LED, a CRT, a polymer dispersed type liquid crystal panel and anorganic EL panel; and a polarization switching device.

Moreover, the polarization switching device may include a ferroelectricliquid crystal panel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a side view and a front view, respectively,illustrating a structure of a conventional optical traffic sign.

FIG. 2A is a diagram schematically illustrating a principle of producinga commonly-employed conventional hologram.

FIG. 2B is a diagram schematically illustrating a principle ofreconstructing the hologram formed as illustrated in FIG. 2A.

Each of FIGS. 3A and 3B is a diagram schematically illustrating aprinciple of producing a conventional reflection-type hologram.

FIG. 3C is a diagram schematically illustrating a principle ofreconstructing the reflection-type hologram formed as illustrated inFIGS. 3A and 3B.

FIG. 3D is a schematic diagram for illustrating a reason why areconstructed image of the reflection-type hologram is blurred.

FIG. 3E is a diagram schematically illustrating the wavelengthdependency of the diffraction efficiency in the reflection-typehologram.

Each of FIGS. 4A and 4B is a diagram schematically illustrating aprinciple of producing a conventional rainbow hologram.

FIG. 4C is a diagram schematically illustrating a principle ofreconstructing the rainbow hologram formed as illustrated in FIGS. 4Aand 4B.

FIG. 4D is a schematic diagram for illustrating a reason why areconstructed image of the rainbow hologram has only little blur.

FIG. 4E is a diagram schematically illustrating the wavelengthdependency of the diffraction efficiency in the rainbow hologram.

Each of FIGS. 5A and 5B is a diagram schematically illustrating aprinciple of producing a reflection-type hologram according to thepresent invention.

FIG. 5C is a diagram schematically illustrating a principle ofreconstructing the reflection-type hologram of the present inventionformed as illustrated in FIGS. 5A and 5B.

FIG. 6A is a schematic diagram for illustrating a reason why areconstructed image of the reflection-type hologram of the presentinvention has only little blur.

FIG. 6B is a diagram schematically illustrating the wavelengthdependency of the diffraction efficiency in the reflection-type hologramof the present invention.

Each of FIGS. 7A and 7B is a diagram schematically illustrating thereflection-type hologram of the present invention formed as illustratedin FIGS. 5A and 5B being reconstructed by using a linear light source.

FIG. 8 is a side view illustrating a structure of an optical displayapparatus according to Embodiment 1 of the present invention.

FIG. 9 is a plan view illustrating the optical display apparatus of FIG.8.

FIG. 10 is a perspective view illustrating an optical system forproducing a hologram according the present invention.

FIGS. 11A and 11B are a side view and a plan view, respectively, of theoptical system for producing a hologram illustrated in FIG. 10.

FIG. 12 is a diagram schematically illustrating the geometricalrelationship between the height of a hologram and the observationposition.

FIG. 13 is a graph illustrating the relationship between the size of areconstructed image and the observation position.

FIG. 14 is a diagram schematically illustrating a structure of anexposure optical system using a one-dimensional diffuser.

FIGS. 15A and 15B are a side view and a plan view, respectively,illustrating a principle of reconstructing the hologram according to thepresent invention.

Each of FIGS. 16A and 16B is a diagram illustrating a shape of anopening which can be used in observing a reconstructed image accordingto the present invention.

FIG. 17A is a perspective view illustrating a reconstruction opticalsystem of the optical display apparatus of the present invention.

FIGS. 17B and 17C are diagrams illustrating viewing angle rangesobtained when a fluorescent tube of the same length is provided in ahorizontal arrangement and a vertical arrangement, respectively.

FIG. 18 is a side view illustrating a structure of an optical displayapparatus according to Embodiment 2 of the present invention.

FIG. 19 is a diagram schematically illustrating that a viewing distancecan be limited.

FIG. 20 is a plan view illustrating the optical display apparatus of thepresent invention where the installation position of a linear lightsource (fluorescent lamp) is spaced apart from the incident plane (whenit is provided in an offset arrangement)

FIG. 21A is a diagram illustrating three exposure pattern masksrespectively corresponding to the three primary colors.

FIG. 21B is a diagram illustrating a reconstructed image obtained bysuperposing the produced three primary color holograms on another.

FIG. 21C is a diagram illustrating the produced holograms being layeredon a single substrate.

FIG. 22 is a graph illustrating the relationship between the change incolor at the center of a reconstructed image and the reference lightangle.

FIG. 23 is a graph illustrating the relationship between the colordistribution in the reconstructed image and the reference light angle.

FIG. 24 is a graph illustrating the relationship between the colordistribution in the reconstructed image and the observation position.

Each of FIGS. 25A to 25E illustrates a diagram illustrating an exemplaryhologram being formed on a flexible substrate.

FIG. 26 illustrates a side view of an optical system for producing ahologram which is reconstructed and displayed with a color having awavelength other than the laser oscillation wavelength.

FIG. 27A is a diagram illustrating an installed hologram in which thechange in color is reduced within the viewing range thereof, and

FIG. 27B is a diagram illustrating a normal hologram beingreconstructed.

FIG. 28 is a conceptual diagram illustrating elementary holograms beingcombined together to produce a large display.

FIGS. 29A and 29B are a front view and a side view, respectively, of anexemplary optical display apparatus in which three display units arearranged side by side.

FIGS. 30A and 30B are diagrams illustrating an exemplary optical displayapparatus in which three display units are arranged side by side fordisplaying a single large pattern, respectively showing separatedreconstructed images and reconstructed images which are seamlesslysynthesized together.

FIG. 31A is a side view illustrating a structure of an optical displayapparatus according to Embodiment 12 of the present invention.

FIG. 31B is a diagram illustrating a pattern which is displayed by theoptical display apparatus of FIG. 31A.

FIG. 31C is a diagram illustrating elementary patterns which arerecorded on the respective display units in the optical displayapparatus of FIG. 31A.

FIG. 31D is a diagram illustrating a reconstructed image which isdisplayed by the optical display apparatus of FIG. 31A.

FIG. 32 is a perspective view of an optical display apparatus accordingto Embodiment 13 of the present invention.

FIG. 33 is a diagram illustrating a structure of a hologram unitincluded in the optical display apparatus of FIG. 32.

FIG. 34 is a diagram illustrating a principle of operation of theoptical display apparatus of FIG. 32.

FIG. 35 is a perspective view of an optical display apparatus accordingto Embodiment 14 of the present invention.

FIG. 36 is a diagram illustrating a structure of a hologram unitincluded in the optical display apparatus of FIG. 35.

FIG. 37 is a diagram illustrating a principle of operation of theoptical display apparatus of FIG. 35.

FIG. 38 is a diagram illustrating a structure of an optical displayapparatus according to Embodiment 15 of the present invention.

FIGS. 39A and 39B are a side view and a plan view, respectively, of anoptical system for producing a transmission-type hologram according toEmbodiment 16 of the present invention.

FIG. 40 is a side view of an optical system for producing areflection-type hologram according to Embodiment 16 of the presentinvention.

FIG. 41 is a side view of an optical system for producing atransmission-type hologram according to Embodiment 17 of the presentinvention.

FIG. 42 is a side view of an optical system for producing areflection-type hologram according to Embodiment 17 of the presentinvention.

FIG. 43 is a side view of an optical system for producing areflection-type hologram according to Embodiment 18 of the presentinvention.

FIG. 44 is a side view of an optical display apparatus according toEmbodiment 19 of the present invention.

FIG. 45 is a diagram schematically illustrating an image projected on ahologram screen in the optical display apparatus of FIG. 44.

FIGS. 46A and 46B are a plan view and a side view, respectively,schematically illustrating a functional principle of the hologram screenin the optical display apparatus of FIG. 44.

FIG. 47 is a diagram schematically illustrating an optical systemproducing a hologram screen in the optical display apparatus of FIG. 44.

FIGS. 48A and 48B are a plan view and a side view, respectively,schematically illustrating how a light beam travels in the opticaldisplay apparatus of FIG. 44.

FIGS. 49A and 49B are a plan view and a side view, respectively,schematically illustrating how a light beam travels from the hologramscreen to the viewer in the optical display apparatus of FIG. 44.

FIG. 50 is a diagram schematically illustrating distortion of aphotographed image obtained by shooting a tall building with a normalcamera.

Each of FIGS. 51A to 51D is a diagram schematically illustrating aprocedure of a front rising photographic technique.

FIG. 52 is a diagram schematically illustrating that the arrangement ofthe optical display apparatus of FIG. 44 satisfies the condition of thefront rising photographic technique.

FIG. 53 is a diagram illustrating an arrangement based on a Scheimpflugcondition, which is a photographic technique.

FIGS. 54A and 54B are a plan view and a side view, respectively,schematically illustrating how a light beam travels in an opticaldisplay apparatus using a varifocal lens.

FIG. 55 is a diagram schematically illustrating an optical system forproducing a hologram screen in an optical display apparatus by which animage is formed on the other side of the hologram screen.

FIG. 56 is a diagram schematically illustrating a structure of anoptical display apparatus by which an image is formed on the other sideof the hologram screen.

FIG. 57 is a diagram schematically illustrating a structure obtainedwhen applying the optical display apparatus of FIG. 56 to a head-updisplay.

FIG. 58 is a diagram schematically illustrating a structure of athree-dimensional display apparatus according to Embodiment 20 of thepresent invention.

FIGS. 59A and 59B are a side view and a front view, respectively, of anexemplary optical display apparatus in which three display units arearranged side by side for displaying a single large pattern.

FIG. 60 is a front view of another exemplary optical display apparatusin which three display units are arranged side by side for displaying asingle large pattern.

FIG. 61 is a side view illustrating a structure of an optical displayapparatus in which a plurality of display units are arranged in a depthdirection of an image for displaying a single large pattern.

Each of FIGS. 62A to 62C is a diagram illustrating an optical system forproducing a hologram screen of each display unit included in the opticaldisplay apparatus of FIG. 61.

FIG. 63A is a diagram illustrating a pattern to be displayed by theoptical display apparatus of FIG. 61.

FIG. 63B is a diagram illustrating elementary patterns which arerecorded on the respective display units in the optical displayapparatus of FIG. 61.

FIG. 63C is a diagram illustrating a reconstructed image displayed bythe optical display apparatus illustrated in FIG. 61.

BEST MODE FOR CARRYING OUT THE INVENTION

Before describing specific embodiments of the present invention, theprinciple of a hologram proposed by the present inventors for realizingan optical display apparatus of the present invention will be described.

To produce a hologram according to the present invention, the hologramplate H1 is first produced by the conventional method as illustrated inFIG. 2A, which is then irradiated with reconstruction illumination light(laser light) RI41, as illustrated in FIG. 2B, in a direction oppositeto that of the reconstruction illumination light RI1 illustrated in FIG.2B and through a slit having a width of Δ, as illustrated in FIG. 5A.Thus, reconstruction light R41, directed from the hologram plate H1 tothe position where the object was located, is reconstructed, therebyreconstructing a real image (reconstructed image) I41 of the object at aposition where the object was located. Then, a hologram dry plate H4 isplaced at a position spaced apart from the reconstructed image I41 ofthe object by a distance Z0, as illustrated in FIG. 5B, and referencelight RL4 is directed to be incident upon the hologram dry plate H4 froman inclined direction opposite from the hologram plate H1. The referencelight RL4 is formed by splitting light emitted from the same laser lightsource as the reconstruction illumination light RI41 by means of a beamsplitter, or the like. Thus, interference fringes between thereconstruction illumination light RI41 and the reference light RL4 arerecorded on the hologram dry plate H4. The hologram dry plate H4 onwhich such interference fringes (having information of the object) arerecorded as a reflection-type hologram will hereinafter be referred toalso as the “reflection-type hologram plate H4”.

FIG. 5C is a diagram schematically illustrating a principle ofreconstructing the rainbow hologram plate H4 formed as described above.

In particular, the hologram plate H4 is irradiated with reconstructionillumination light (white light) RI42 which propagates in a directiondiametrically opposite to that of the reference light RL4 illustrated inFIG. 5B. Thus, reconstruction light R42 having information of the objectrecorded on the hologram plate H4 is reconstructed and directed towardthe position where the slit was located during the hologram production,so as to form a reconstructed image I42 at a position where the objectwas originally located.

With a hologram of the present invention formed as described above, thereconstructed image I42 to be observed is clearer as compared to thatobserved by the conventional reflection-type hologram, without theproblem of a substantial change in the color of the reconstructed imagedepending upon the observation position as in the conventional rainbowhologram. The reason for this will be described below.

The reconstruction illumination light directed toward the hologram ofthe present invention is white light. Therefore, wavelengths other thana wavelength λ0 of the laser light used to produce the hologram are alsocontained in the reconstruction illumination light. However, areflection-type has a high wavelength selectivity, as shown in a graphof FIG. 6B illustrating the wavelength dependency of the diffractionefficiency, whereby substantially none of light having a wavelength faraway from the wavelength (center wavelength) λ0 of the laser light usedto produce the hologram is diffracted. Therefore, basically, only lighthaving a wavelength close to the center wavelength λ0 is diffracted tobe the reconstruction light R42, thereby reconstructing the image I42from such light. In practice, other reconstructed images areconcurrently formed from light having a wavelength which is close to,but different from, the center wavelength λ0, as represented by λ1 andλ2 in FIGS. 6A and 6B. However, since the present invention uses a slitwhen producing a hologram, the reconstructed images formed by thedifferent wavelengths of light are formed at respectively differentpositions (i.e., spatially separated from one another). For example,reconstructed images formed by light having wavelengths which aredifferent from the center wavelength λ0, as represented by λ1 and λ2 inFIGS. 6A and 6B, are formed concurrently at positions different fromthat of the reconstructed image formed by light having the centerwavelength λ0, but are not spatially superimposed on the intendedreconstructed image formed by the light having the center wavelength λ0.Therefore, with the hologram of the present invention, although thecolor of the reconstructed image I42 slightly changes as the observationposition changes, the reconstructed image I42 of each color is clearlyobserved.

The hologram of the present invention is of a reflection-type, and thushas a high wavelength selectivity in the diffraction efficiency, wherebylight having a wavelength other than those closer to the centerwavelength λ0 is not diffracted. Therefore, where white light from apoint light source spaced apart from the rainbow hologram plate H4 by acertain distance is used as the reconstruction illumination light, whenthe observation position changes substantially (i.e., when the observermoves substantially), the diffraction efficiency of the hologram for thewavelength which forms an image which can be observed from theobservation position becomes zero, whereby no reconstructed image isobserved. In other words, the viewing range for the reconstructed imageI42 is extremely narrowed when the hologram of the present invention isreconstructed by collimated light RI42A from a point light source.

However, when the reconstruction illumination light RI42 to be incidentupon the hologram plate H4 is not collimated light but is a group oflight beams having respective incident angles, as illustrated in FIG.7A, the reconstructed images I42 are reconstructed at spatiallydifferent positions by beams of reconstructed light R42 having mostsuitable wavelengths for the respective incident angles. Such anincident condition can be realized by using a linear light source LLrather than a point light source. In particular, when the linear lightsource LL such as a fluorescent lamp is used as the light source LL ofthe reconstruction illumination light RI42 for the hologram of thepresent invention, as illustrated in FIG. 7B, it is possible tointentionally provide a certain angle range to the incident angle of thereconstruction illumination light RI42 for the hologram plate H4,thereby widening the viewing range for the reconstructed image I42.

Then, when the observation position for the hologram of the presentinvention changes, the color of the reconstructed image I42 changes asin the case of the conventional rainbow hologram. However, the rate ofsuch change in the color of the reconstructed image I42 is as small asseveral % with respect to the color change of a rainbow hologram. Forexample, where a hologram plate is formed with reference light of anincident angle of 45°, the wavelength changes on the order of 100 nm fora change in the observation position for a rainbow hologram such thatthe color of the reconstructed image changes from blue to red. On thecontrary, for the hologram of the present invention, the wavelength ofthe reconstructed image I42 changes by about 6 nm for a similar changein the observation position, whereby substantially no color change isrecognized.

When the structure of the hologram of the present invention as describedabove is applied to a conventional rainbow hologram, reconstructedimages of seven colors overlap one another, thereby whitening theoverall image. This is because the conventional rainbow hologram is atransmission-type hologram, whereas the hologram of the presentinvention is of a reflection type and thus has a high wavelengthdependency of the diffraction efficiency.

Thus, the principle of forming a hologram of the present invention takesadvantage of the characteristic of a reflection-type hologram of “a highwavelength dependency of the diffraction efficiency and thus a narrowviewing range for the reconstructed image”, which was considered as adisadvantage of the conventional reflection-type hologram, and forms ahologram plate by recording, as a reflection-type hologram, an imagereconstructed by laser light which has passed through a slit. When areconstructed image is obtained by using a hologram plate formed asdescribed above, it is possible to obtain characteristics which were notobtained by various conventional hologram forming principles, e.g.: theimage is not substantially blurred even when the observation position isshifted; and the wavelength selectivity is high so that it is possibleto obtain a color reconstructed image by superimposing reconstructedimages on one another.

Hereinafter, various embodiments of optical display apparatusesaccording to the present invention which are provided by using thehologram method of the present invention which is based on theabove-described principle.

Embodiment 1

FIG. 8 is a side view illustrating a structure of an optical displayapparatus according to Embodiment 1 of the present invention, and FIG. 9is a plan view of the optical display apparatus. In this embodiment, theoptical display apparatus of the present invention is used as a trafficsign in a tunnel.

In FIG. 8, reference numeral 1 denotes an optical display apparatus ofthe present embodiment; 2 a hologram; 3 a fluorescent lamp as a linearlight source; 4 fluorescent lamp fittings, and 5 a shield plate. Theoptical display apparatus 1 is provided on a ceiling plane 7 of a tunnel6.

A portion of illumination light 8 emitted from the fluorescent lamp 3 isincident upon the hologram 2, and is diffracted by the hologram 2 so asto become reconstructed light 9, thus forming a reconstructed image 11on a virtual display plane 10. Then, the reconstructed image 11 asviewed from the front side thereof is viewed from a car running throughthe tunnel 6 as if it were hung at a position downwardly spaced apartfrom the ceiling plane 7 of the tunnel 6. However, this is only adisplay (the reconstructed image 11) on the virtual display plane 10,and there is no object actually existing at the position. Therefore,there is no chance for a car collision.

The virtual display plane 10 is a plane or a curved surface which isvirtually provided in a space. The reflected light from the surface ofthe hologram 2 can be deflected in a direction toward the road surface(reflected light in this direction is shown in FIG. 8) or in a directiontoward the ceiling plane 7 (reflected light in this direction is notshown in FIG. 8), whereby the reflected light will not be directlyincident upon the driver's eye. Rather, the reflected light iseffectively used as illumination light for illuminating the road surfaceor the ceiling plane.

Moreover, a portion of the illumination light 8 from the fluorescentlamp 3 is shielded by the shield plate 5, whereby it will not bedirectly incident upon the driver's eye. Other portions of theillumination light 8 directed directly toward the road surface or theceiling plane can also be effectively used as illumination light forilluminating the road surface or the ceiling plane.

The light source section including the fluorescent lamp 3 and thefluorescent lamp fittings 4 may be provided by using common lampfittings as those used in houses or offices, but it is preferred to makeit waterproof so that water does not get into it during a tunnelclean-up. For example, the light source section can be provided byembedding the fluorescent lamp 3 and the fluorescent lamp fittings 4into the ceiling plane 7 of the tunnel 6, and covering them with atransparent cover.

Next, a principle by which the hologram 2 forms the reconstructed image11 on the virtual display plane 10 will be described in association witha method for producing the same.

First, a method for producing the hologram 2 will be briefly describedwith reference to FIG. 10.

FIG. 10 is a perspective view illustrating an optical system forproducing the hologram 2, wherein reference numeral 12 denotes a slit,13 a pattern mask for a traffic sign indicating a speed limit, 14 objectlight, 15 an incident plane, 16 reference light, and 17 a hologram dryplate. Although the optical system illustrated in FIG. 10 is arranged ina horizontal arrangement where it is laid horizontally at 90° since theproduction optical system is normally arranged on an optical table, avertical arrangement is illustrated herein according to the arrangementused during an operation of the optical display apparatus. Moreover, inpractice, a pattern mask having a plurality of different patterns isused corresponding to the three primary colors, and the hologram isproduced by appropriately switching the wavelength of the laser forexposure and the arrangement of the optical system. However, for thesake of simplicity, an arrangement having the single pattern mask 13will be described herein.

A method for producing the hologram 2 is as follows.

First, argon laser light having a wavelength of 514.5 nm, which has beentransmitted through a ground glass to be diffused light, is directed tobe incident upon the slit 12. Information of the pattern mask 13 is readby the light having passed through the slit 12, so as to form the objectlight 14. This arrangement is intended to show the reconstructed imageas if it is floating, and the pattern mask 13 is placed to befront-sided as viewed from the slit 12 side. The slit to be used has awidth of about 1.5 mm, and a length of about 40 mm, for example.

The substantially collimated reference light 16 emitted from the argonlaser is directed to be incident upon incident plane 15 which isuniquely defined as a plane vertical to the longitudinal direction ofthe slit 12. Herein, the reference light 16 is directed to be incidentat an angle of 15° from the reverse side of the hologram dry plate 17 toform a reflection hologram. Although it is not necessarily required thatthe reference light 16 is incident upon the incident plane 15, anarrangement where the reference light 16 is incident upon the incidentplane 15 is depicted herein as a more preferred embodiment.

Thus, the object light 14 and the reference light 16 form interferencefringes, and the interference fringes are recorded on the hologram dryplate 17. A silver salt, a dichromate gelatin, a photopolymerizablephotopolymer, or the like, is typically used as a material of thehologram dry plate 17. For example, a dry-film type photopolymerizablephotopolymer having a thickness of about 20 μm is attached to a glasssubstrate so as to provide the hologram dry plate 17.

Next, the method for producing the hologram 2 will be described ingreater detail.

FIGS. 11A and 11B are a side view and a plan view, respectively, of theoptical system for producing a hologram illustrated in FIG. 10.Reference numeral 18 denotes a ground glass, 19 laser light, and 20diffused light.

As illustrated in FIG. 11A, the laser light 19 is incident upon theground glass 18 so as to be the diffused light 20 and then incident uponthe slit 12. The slit 12 has a narrow width as viewed from a sidethereof, and transmits only a portion of the diffused light 20.Therefore, light having passed through the slit 12 as viewed form theside appears as spread light coming from a single point. This lightreads the information of the pattern mask 13, and irradiates thehologram dry plate 17 as the object light 14. This can be considered asprojection of the pattern mask 13 onto the hologram dry plate 17. Theobject light 14 including the information of the object formsinterference fringes with the reference light 16 incident upon thereverse side of the hologram dry plate 17, and the interference fringesare recorded on the hologram dry plate 17.

At this time, the “shadow” of the pattern mask 13 projected onto thehologram dry plate 17 has been enlarged. In view of the rate ofprojection magnification, the pattern mask 13 is produced while beingshrunk in one direction. Although the rate of magnification variesdepending upon the setting of the optical system, it normally is about1.2 to about 2.

More specifically, assuming the original height of the pattern mask 13to be Hm, and the height of the image actually viewed from theobservation position OP to be Hi, the rate of magnification is expressedas follows based on the geometric relationship shown in FIG. 12:

Hi=Hm(1−z 0/L′)/(1−z 0/L).

Herein, z0 denotes the distance from the hologram dry plate 17 to theimage (the pattern mask 13), L denotes the distance from the hologramdry plate 17 to the slit 12 during the hologram production, and L′denotes the distance from the hologram dry plate 17 to the observationposition OP. As can be seen from this, the rate of magnification is 1when L=L′; i.e., there is no enlargement/shrinkage effect when the imageis observed from the position where the slit 12 was located. On theother hand, an enlargement/shrinkage effect is provided when thedistance L′ changes, i.e., when the image is observed from a wide areaaway from the position where the slit 12 was located.

This relationship is illustrated in FIG. 13 as the relationship betweenthe normalized observation distance (L′/L) and the normalized imageheight (Hi/Hm), using L/z0 as a parameter. This shows that the valueL/z0 may be increased in order to reduce the change in the rate ofmagnification experienced when the image is viewed from a wide area. Therate of magnification can be suppressed to be 1.1 or less (i.e., achange in shape of 10% or less) even when the image is viewed from awide area, preferably by setting L/z0 to be 10 or more.

More preferably, if the value L/z0 is selected to be substantiallyinfinite, the change in the rate of magnification would be substantiallyeliminated. Back to the definition, selecting the value L/z0 to besubstantially infinite means that, excluding the case where z0=0, theline extending from the slit 12 to the hologram dry plate 17 has nogradient. Therefore, the slit 12 and the ground glass 18 may be replacedwith a one-dimensional diffuser 1001 which has a light diffusing effectonly in the width direction of the hologram dry plate 17 with no lightdiffusing effect in the height direction of the hologram dry plate 17,as illustrated in FIG. 14. There are a number of examples for such adiffuser 1001, including those using a diffraction grating, or thosewhich are holographically produced, or a lenticular lens sheet having anarray of cylindrical lenses may alternatively be used.

Now, the method for producing a hologram using the slit 12 and theground glass 18 will be further described.

As illustrated in the plan view of FIG. 11B, the slit 12 has a largewidth as viewed from the above, and transmits the diffused light 20coming from the ground glass 18 over a wide range. In FIG. 11B, diffusedlight having passed through the central portion of the slit 12 isindicated by a solid line, while diffused light having passed through anend portion of the slit 12 is indicated by a broken line. Information ofthe pattern mask 13 obtained when viewed from the front side thereof isprojected onto the hologram dry plate 17 by the diffused light indicatedby the solid line, whereas information of the pattern mask 13 obtainedwhen viewed from a slightly inclined direction through the end portionof the slit 12 is projected onto the hologram dry plate 17 by thediffused light indicated by the broken line. The object light 14including such information forms interference fringes with the referencelight 16 incident upon the reverse side of the hologram dry plate 17,and the interference fringes are recorded on the hologram dry plate 17.This is the principle of how reconstructed images of the pattern mask 13as viewed from different angles are formed on the respective eyes of theobserver when the hologram is reconstructed.

Although side views and plan views have been separately described in theabove for simplicity, it is understood that the interference fringes aresimultaneously recorded in an actual hologram producing process.

Now, a principle of reconstructing the hologram of the present inventionwill be described.

The illumination light used to reconstruct a hologram is typicallyconjugate light of reference light. Since in the process of producing ahologram of the present invention, the reference light is collimatedlight as described above, the illumination light may also be collimatedlight. However, although collimated light can be easily provided whenproducing a hologram because laser light is used, it is difficult toprovide collimated light from a white light source such as a halogenlamp which is typically used for reconstructing a hologram. Practically,a light source with a small light-emitting section is selected, whilelimiting the aperture thereof, for reconstructing a hologram. Such alight source, which can be considered substantially as a point lightsource, is arranged sufficiently away from the hologram, so as toilluminate the hologram with diffused light which can be considered assubstantially collimated light. The image of the hologram 2 of thepresent embodiment can generally be reconstructed by such a method.

FIGS. 15A and 15B are a side view and a plan view, respectively,illustrating a principle of reconstructing the hologram 2. Referencenumeral 21 denotes a halogen lamp, 22 an opening, 23 illumination light,24 reconstructed light, 25 an observer, and 26 a reconstructed image ofthe slit 12.

Light emitted from the halogen lamp 21 is limited by the opening 22, soas to form the illumination light 23 which can be considered assubstantially collimated light. The reconstructed light 24 formed bydiffracting the illumination light 23 with the hologram 2 forms thereconstructed image 11 on the virtual display plane 10, i.e., in thevicinity of the position where the pattern mask 13 was located whenproducing the hologram, whereby the observer 25 views the reconstructedimage 11 as if it is floating apart from the hologram plane.

As a result of an observation, the viewing angle in the horizontaldirection for which the reconstructed image 11 can be observed is about8°, which means that the display provided by the optical displayapparatus 1 of the present invention can be recognized from a car at adistance of 50 m to 100 m away from the display even if the car changeslanes (i.e., moves in the horizontal direction by about 6 m) on anactual road. However, the viewing angle in the vertical direction is assmall as about 1°, which means that it may not be possible to ensure asufficient zone or time for which the sign can be recognized from a carmoving at a high speed.

Moreover, the reconstructed image 11 appears to be brightest when theobserver is at the position where the reconstructed image 26 of the slit12 is formed, i.e., the position where the slit 12 was located whenproducing the hologram, and the entire reconstructed image 11 can beseen when the observer is in the vicinity of such a position. However,only a portion of the image can be seen when the observer moves from theposition toward the hologram 2 or away from the hologram 2.

The above observation result shows that although a reconstructed imagecan be obtained but it is extremely difficult to provide a practicaltraffic sign for tunnels by reconstructing it with a point light source.

Therefore, the present inventors continued to study the positionalrelationship between the light source and the hologram, and theinteraction between the illumination light and the hologram, andconducted a more detailed observation of the reconstructed image,thereby discovering a unique practical advantage which is extremelyimportant to solving the above-described problems and providing theoptical display apparatus 1 of the present invention.

FIGS. 16A and 16B illustrate two characteristic shapes for the opening22 used during the above-described observation of the reconstructedimage.

As a result of the observation, while the reconstructed image of thehologram 2 was blurred when the width of the opening 22 was widened inthe horizontal direction as illustrated in FIG. 16A, while thereconstructed image of the hologram 2 was not blurred when the length ofthe opening 22 was extended in the vertical direction as illustrated inFIG. 16B. Moreover, the viewing range in the vertical direction wasincreased as the length of the opening 22 was extended, with the colorof the reconstructed image being unchanged within the viewing range.That is, the observer always observes an image of the same color whichis not blurred within the viewing range. This is a significant advantageprovided by providing the hologram 2 with a reflection-type hologram.

When the opening 22 which is elongated in the vertical direction isused, the entire reconstructed image can be observed even when theobserver moves from the position where the reconstructed image 26 of theslit 12 is formed toward the hologram 2 or away from the hologram 2.That is, the observer sees the entire, unblurred image of the same colorwithout any portion thereof being cut out even when the observer changesposition with respect to the image in the depth direction.

Although the expression “the color does not change” is used herein,strictly speaking, the reconstructed wavelength changes. However, thechange in wavelength can be suppressed to a level such that it cannot beperceived by a human eye, by appropriately selecting the parameters ofthe hologram.

The above-described observation result means that it is possible tosolve all of the above-described problems and to provide a practicaltraffic sign for tunnels by employing a combination of the hologram 2and the vertically-elongated opening 22 of the present invention.

The straight tube fluorescent lamp 3 is used as a light source inEmbodiment 1 of the present invention, as illustrated in FIG. 8. Evenwhen the image is reconstructed with the straight tube fluorescent lamp3, an unblurred, bright reconstructed image with no change in color canbe obtained. Moreover, an unblurred reconstructed image can always berecognized even when observing the hologram 2 as by viewing it from anupward or downward direction. As the fluorescent lamp 3 is broughtslightly closer to the hologram 2 under a predetermined condition, theviewing angle in the vertical direction may reach ±5°, which impliesthat it is possible to ensure a sufficient zone and time for which thesign can be recognized from a car moving at a high speed. Moreover, thereconstructed image will not be cut off even when the distance from thehologram 2 changes, whereby the reconstructed image can be seensufficiently before the optical display apparatus 1.

While the reference light 16 is directed to be incident upon theincident plane 15 in the process of producing the hologram, the presentinvention is not limited thereto. Moreover, while the fluorescent lampis arranged on the incident plane 15 for reconstructing the image, thepresent invention is not limited thereto. According to the presentinvention, the incident direction of the reference light and thearrangement and direction of the linear light source each have somedegree of tolerance.

Moreover, for the method of producing a hologram using the diffuser1001, the incident plane can be defined as a plane perpendicular to thedirection in which the diffused light is spread. While the referencelight is directed to be incident upon the incident plane in the basicarrangement, the present invention is not limited thereto. Moreover,although the fluorescent lamp is arranged on the incident plane forreconstructing the image in the basic arrangement, the present inventionis not limited thereto.

Embodiment 2

While the fluorescent lamp 3, which is a linear light source, ishorizontally arranged in Embodiment 1, the installation condition of thefluorescent lamp 3 is not limited in terms of the orientation thereof aslong as it is basically placed in a position on the incident plane 15 orin the vicinity of such a position.

FIG. 17A is a perspective view illustrating a reconstruction opticalsystem of the optical display apparatus of the present invention,wherein the system may be arranged in either one of the horizontal andvertical arrangements illustrated, or at any intermediate angletherebetween. However, the viewing angle range in the vertical directionvaries depending upon the installation direction.

FIGS. 17B and 17C are diagrams for comparing the viewing angle rangesobtained when a fluorescent tube of the same length is provided in thehorizontal arrangement and the vertical arrangement.

In the case of the horizontal arrangement of FIG. 17B, illuminationlight 28 emitted from the right end of a fluorescent lamp 27 isdiffracted by the hologram 2, thereby forming a reconstructed image 29,which is recognized by an observer 30. On the other hand, illuminationlight 31 emitted from the left end of the fluorescent lamp 27 isdiffracted by the hologram 2, thereby forming a reconstructed image 32,which is recognized by an observer 33. The angle formed by the positionof the observer 30 and that of the observer 33 with respect to thehologram 2 is the viewing angle range for the horizontal arrangement.

In the case of the vertical arrangement of FIG. 17C, illumination light34 emitted from the lower end of the fluorescent lamp 27, which isindicated by a solid line, is diffracted by the hologram 2, therebyforming a reconstructed image 35, which is recognized by an observer 36.On the other hand, illumination light 37 emitted from the upper end ofthe fluorescent lamp 27 is diffracted by the hologram 2, thereby forminga reconstructed image 38, which is recognized by an observer 39. Theangle formed by the position of the observer 36 and that of the observer39 with respect to the hologram 2 is the viewing angle range for thevertical arrangement.

A comparison between the horizontal arrangement and the verticalarrangement shows that a larger viewing angle can be obtained with thevertical arrangement. From a different point of view, a shorterfluorescent lamp can be used when employing an arrangement close to thevertical arrangement. Strictly speaking, it is more preferred to arrangethe fluorescent lamp to be perpendicular to the optical path for thereconstruction illumination light.

FIG. 18 is a side view illustrating a structure of an optical displayapparatus according to Embodiment 2 of the present invention. Also inthis embodiment, the optical display apparatus of the present inventionis used as a traffic sign in a tunnel.

In FIG. 18, reference numeral 40 denotes the optical display apparatusof the present embodiment, 41 a fluorescent lamp, which is a linearlight source, 42 fluorescent lamp fittings, and 43 a reflecting plate.The optical display apparatus 40 is provided on the ceiling plane 7 ofthe tunnel 6.

Direct light emitted from the fluorescent lamp 41 and indirect lightwhich has been once reflected by the reflecting plate 43 are synthesizedtogether, thereby forming illumination light 44. The effect of thereflecting plate 43 makes possible an even brighter display. A portionof the illumination light 44 which is incident upon the hologram 2 isdiffracted by the hologram 2 to be reconstructed light 45, therebyforming the reconstructed image 11 on the virtual display plane 10.Then, the reconstructed image 11 as viewed from the front side thereofis viewed from a car running through the tunnel 6 as if it were atraffic sign indicating a speed limit hung at a position downwardlyspaced apart from the ceiling plane 7 of the tunnel 6. However, this isonly a display (the reconstructed image 11) on the virtual display plane10, and there is no object actually existing at the position. Therefore,there is no chance for a car collision.

The virtual display plane 10 is a plane or a curved surface which isvirtually provided in a space. The reflected light from the surface ofthe hologram 2 can be deflected in a direction toward the road surface(reflected light in this direction is shown in FIG. 18) or in adirection toward the ceiling plane 7 (reflected light in this directionis not shown in FIG. 18), whereby the reflected light will not bedirectly incident upon the driver's eye. Rather, the reflected light iseffectively used as illumination light for illuminating the road surfaceor the ceiling plane.

Moreover, a portion of the illumination light 44 from the fluorescentlamp 41 is shielded by the fluorescent lamp fittings 42 and/or thereflecting plate 43, whereby it will not be directly incident upon thedriver's eye. Other portions of the illumination light 44 directeddirectly toward the road surface or the ceiling plane can also beeffectively used as illumination light for illuminating the road surfaceor the ceiling plane.

The light source section including the fluorescent lamp 41 and thefluorescent lamp fittings 42 may be provided by using common lampfittings as those used in houses or offices, but it is preferred to makeit waterproof so that water does not get into it during a tunnelclean-up. For example, the light source section can be provided bycovering the fluorescent lamp 41 and the fluorescent lamp fittings 42with a transparent cover.

Embodiment 3

The viewing range can be intentionally limited by utilizing theabove-described characteristic that the viewing angle range is dependentupon the length of the fluorescent lamp and the direction in which thefluorescent lamp is arranged. For example, by appropriately setting thelength of the fluorescent lamp and the direction in which thefluorescent lamp is arranged, it is possible to realize an arrangementsuch that the traffic sign becomes visible at a distance of 100 m beforethe sign and becomes invisible at a distance of 50 m before the sign, asillustrated in FIG. 19.

This arrangement can be practiced with an optical display apparatus ofany of the embodiments described in this specification.

Embodiment 4

FIG. 20 is a plan view illustrating an optical display apparatus of thepresent invention where the installation position of the fluorescentlamp 46 is spaced apart from the incident plane 15.

A reconstructed image 48 can be well recognized also in this case thoughit is associated with a slight change in color and a slight reduction inthe viewing angle range. However, the observer 49 needs to observe theimage from a position moved from the incident plane 15 in a directionopposite to the direction in which the fluorescent lamp 46 is moved fromthe incident plane 15, as illustrated in FIG. 20. This is becauseillumination light 47 is incident upon the hologram 2 in an inclineddirection, whereby the reconstructed image 48 is formed at a positionspaced apart from the incident plane 15. The above-described arrangementcan be positively used for display, when it is difficult to install thefluorescent lamp 46 on the incident plane 15 for reasons such as forsaving the installation space for the optical display apparatus. It isunderstood that it is possible to intentionally produce hologram in viewof such a reconstruction arrangement.

This arrangement can be practiced with an optical display apparatus ofany of the embodiments described in this specification.

Embodiment 5

only the process for a single pattern mask and the reconstruction of ahologram produced by such a process have been described above. This maysuffice for a single color display. However, for producing a colordisplay, a hologram is produced by layering different pattern maskscorresponding to the colors to be displayed on one another so as torealize the color display.

FIG. 21A illustrates three exposure pattern masks corresponding to thethree primary colors. These pattern masks are used as objects so as toproduce single-color holograms of R, G and B, respectively. FIG. 21Billustrates a reconstructed image obtained by superposing the threeproduced holograms on one another. FIG. 21C illustrates the producedholograms being layered on a single substrate.

The useful characteristic of the hologram described in the embodimentsof the present invention, i.e., the characteristic that the color of thereconstructed image does not change within the viewing range even whenthe vertical opening limit width is widened, holds for various colors.Therefore, the color of the color reconstructed image of the layeredhologram does not change within the viewing range (strictly speaking,the reconstructed wavelength slightly changes, but the change inwavelength cannot be perceived by a human eye as a substantial change incolor). The change in the reconstructed wavelength at the center of thereconstructed image depends upon the incident angle θ of the referencelight which is set when producing the hologram of each color, asillustrated in the wavelength shift ratio with respect to the incidentangle θ of the reference light (ΔλR/ΔλT) in FIG. 22. In particular, thechange in color increases as the incident angle θ of the reference lightincreases. However, in the case where the incident angle of thereference light θ=30°, for example, the change in color (the change inwavelength) within a viewing angle range of ±2°, which is required for asign, is about 4 nm, which cannot be substantially perceived by a humaneye. Therefore, for a commonly-employed incident angle of the referencelight, θ=45° or less, the reconstructed image is perceived as having asingle color.

The wavelength shift ratio with respect to the incident angle θ of thereference light (ΔλR/ΔλT), as illustrated in FIG. 22, denotes the ratioof the amount of wavelength shift ΔλR for the arrangement of the presentinvention, which is a reflection-type hologram, with respect to theamount of wavelength shift ΔλT for a transmission-type hologram such asthe conventional rainbow hologram.

More strictly, when a color distribution exists in the reconstructedimage, and the incident angle θ of the reference light increases, thecolor distribution increases. This relationship is illustrated in FIG.23 as the relationship between the reference light angle and thereconstructed wavelength width. Herein, H denotes the height of thehologram. FIG. 23 shows that by selecting the parameter L/H to be alarge value, it is possible to reduce the color distribution to anunrecognizable level within the range of the incident angle of thereference light, θ=45° or less.

The color distribution in the reconstructed image also changes dependingupon the observation position. In particular, the change in colorincreases as the observation position moves farther away. Thisrelationship is illustrated in FIG. 24 as the relationship between thenormalized observation position and the reconstructed wavelength width.This shows that by appropriately selecting the parameter L/H, it ispossible to reduce the color distribution to an unrecognizable level.

More preferably, if the value L/H could be selected to be substantiallyinfinite, the change in the rate of magnification would be substantiallyeliminated. Back to the definition, selecting the value L/H to besubstantially infinite means that the line extending from the slit tothe hologram has no gradient. Therefore, the slit and the ground glassmay be replaced with a one-dimensional diffuser which has a lightdiffusing effect only in the width direction of the hologram with nolight diffusing effect in the height direction of the hologram. Thereare a number of examples for such a diffuser, including those using adiffraction grating, or those which are holographically produced. Forexample, a lenticular lens sheet having an array of cylindrical lensesmay be used.

The arrangement of the exposure optical system to be used in such a caseis as described above with reference to FIG. 14.

The arrangement of the present embodiment as described above can bepracticed with an optical display apparatus of any of the embodimentsdescribed in this specification.

Embodiment 6

The hologram 2 of the present invention can be layered with a flexiblesubstrate which can be bent, rolled, or folded, as illustrated in FIGS.25A to 25C, respectively.

While a hologram dry plate is formed by attaching a dry film typephotopolymer to a glass substrate in the above-described process ofproducing the hologram 2, the photopolymer on which a hologram image hasbeen recorded can be detached from the glass substrate and re-attachedto another substrate after the process. The hologram 2 of the presentinvention can be bent, rolled or folded, as illustrated in FIGS. 25A to25C, respectively, after it is re-attached to another flexiblesubstrate, including but not limited to, a plastic film, paper, cloth,or the like. This allows for compact storage of the display apparatusnot being used, and such a display apparatus can easily be carriedaround.

In such a case, it is not necessary to carry around the light source.This is because it is very easy to find a place where a fluorescent lampis used, and the reconstructed image can easily be obtained by simplyunfolding the hologram in the vicinity of a fluorescent lamp which isused in a house, an office, a train station, a train car, an elevator,or the like. Thus, the hologram of the present invention can beeffectively used as a poster, a direction board, a billboard, etc., aswell as in various other applications. Moreover, regarding theinstallation, it can be adequately installed simply by attaching it to awall surface by common means such as a pushpin, a tape, or the like. Theembodiment as described above is made possible because according to thepresent invention, the reconstructed image of the hologram can bedisplayed with a fluorescent lamp, which is one of the mostcommonly-employed light sources.

Moreover, the hologram can be provided in the form of a film or a bookby superposing a plurality of holograms on one another. In such a case,reconstructed images can be viewed under a fluorescent lamp as byturning over pages of a book, and such a hologram can be effectivelyused as a trade catalog, a picture book, a map, etc., as well as invarious other applications.

Moreover, it is possible to reconstruct a continuous image by recordingthe image on a looped flexible substrate as illustrated in FIG. 25D andby moving the same by means of a roll. Alternatively, it can be providedin a wind-up form as illustrated in FIG. 25H.

The arrangement of the present embodiment where a hologram is layered ona flexible substrate as described above can be practiced with an opticaldisplay apparatus of any of the embodiments described in thisspecification.

Embodiment 7

A laser typically used as an exposure laser includes an argon laser or akrypton laser, each having primary oscillation wavelengths of 488 nm,514.5 nm and 467.1 nm. Through exposure with the three wavelengths, itis possible to reconstruct and display colors of the wavelengths.However, the following process is generally required to reconstruct anddisplay colors of wavelengths other than the oscillation wavelength ofthe laser, e.g., to display green at 550 nm, to which a human eye hasthe highest visibility, or to display yellow in the vicinity of 570 nm.

Where a silver salt is used as the hologram material, the sample isexposed with an argon laser at 514.5 nm, and then immersed in anappropriate solution, so as to widen the interval of the periodicarrangement of the hologram, thereby shifting the reconstructedwavelength to 550 nm or 570 nm. Alternatively, where a dry film typephotopolymer is used, the sample is similarly exposed with an argonlaser at 514.5 nm, and then the entire surface of the sample isirradiated with UV light, after which a color tuning film is layered onthe sample, followed by a heat treatment. The movement of a swellingsubstance from the color tuning film to the photopolymer side widens theinterval of the periodic arrangement, thereby shifting the reconstructedwavelength to 550 nm or 570 nm. In any case, such a method is notpreferable in view of improving the production efficiency because it isnecessary to perform an additional process after laser exposure.

On the contrary, for the hologram of the optical display apparatus ofthe present invention, It is possible to shift the reconstructed colorby setting the reference light and the object light so that they areincident upon the hologram dry plate at an appropriate angle during thelaser exposure, without subsequently performing the additional process.

FIG. 26 illustrates a side view of an optical system for producing ahologram which is reconstructed and displayed with a color having awavelength other than the laser oscillation wavelength. Unlike theoptical system illustrated in FIG. 15A, a hologram dry plate 50 isinclined by an angle θobj with respect to the optical axis of the objectlight. A pattern mask 51, which is an object, is similarly inclined bythe angle θobj. The pattern mask 51 is produced while being furthershrunk in one direction as compared to the above-described pattern mask13. Strictly speaking, the pattern mask 51 is not produced with auniform shrinkage rate, but with a shrinkage rate which continuouslyvaries for various positions of the pattern mask 51. On the other hand,reference light 52 is arranged to be incident upon the reverse side ofthe hologram dry plate 50 at an angle θref.

Where the exposure is performed with laser light at a wavelength λ=514.5nm, for example, using such a producing optical system, a reconstructedimage of bright green at a wavelength λE=550 nm can be observed over thefront surface of the hologram dry plate during reconstruction by settingthe object light angle θobj and the reference light angle θref to be−25.3° and 42.1°, respectively. Then, the incident angle of theillumination light having a wavelength of 550 nm is 15°.

Where the exposure is similarly performed with laser light at awavelength λ=514.5 nm, a reconstructed image of bright yellow at awavelength λE=570 nm can be observed over the front surface of thehologram dry plate during reconstruction by setting the object lightangle θobj and the reference light angle θref to be −33.1° and 51.2°,respectively. Then, the incident angle of the illumination light havinga wavelength of 570 nm is also 15°.

The above-described angle can be determined from the following relation:

θRE=sin⁻¹ [n·sin{(θ0+θR)/2+π−φ}]; and

θOE=sin⁻¹ [n·sin{(θ0+θR)/2+φ}].

Herein, θRE and θOE are the incident angles of the illumination lightand the reconstructed light, respectively, for the wavelength to bedisplayed. π denotes the ratio of the circumference of a circle to itsdiameter, and n denotes the average refractive index of the hologrammaterial. Herein, the calculation was conducted with n=1.52. Moreover,θR, θO and φ are parameters which are respectively expressed as follows:

 θO=sin⁻¹(sin θobj/n);

θR=sin⁻¹(sin θref/n)−π; and

φ=sin⁻¹[λ sin {(θ0−θR)/2}/E].

Thus, it is possible to display any intermediate color by using ahologram which has been produced so as to exhibit a desiredreconstructed wavelength in combination with a light source having acontinuous emission distribution, e.g., a white fluorescent lamp.Moreover, it is possible to display a bright reconstructed image with ahigh light efficiency by combining it with a light source having threeemission peaks, corresponding to the three colors of R, G and B, e.g., athree-wavelength fluorescent clamp.

The arrangement of the above-described embodiment as described above canbe practiced with an optical display apparatus of any of the embodimentsdescribed in this specification.

Embodiment 8

As described above in Embodiment 5 of the present invention, as thefield of view of the observer is moved in the vertical direction, thereconstructed wavelength slightly changes. Assuming that the objectlight is incident upon the hologram from the front side thereof whileproducing the hologram, the degree of the change in color depends uponthe set incident angle θ of the reference light, and the change in colorincreases as θ increases. For example, when θ exceeds 45°, a change inthe reconstructed wavelength of 6 nm or more occurs in the center of thereconstructed image within the viewing angle range of ±2°, which isrequired for a sign, whereby even a human eye recognizes a slight changein color in the portion where the change in hue is substantial.Moreover, the color distribution within the image becomes moresignificant.

While a method for producing a hologram by optimally selecting theparameter L/H to suppress such a change has already been described abovein Embodiment 5, there exists a hologram setting angle, for the hologramof the optical display apparatus of the present invention, with which itis possible to minimize the change in color after production. Thesetting angle is an angle which is substantially ½ of the angle betweenthe illumination light and the object light; and more exactly an anglewhich satisfies the following relation:

θac=sin⁻¹ [n·sin {(θ0+θR+π)/2}].

For example, when the exposure wavelength is 514.5 nm, with the incidentangle of the reference light being θref=45° and the incident angle ofthe object light being 0°, θac=21.4° is obtained from the aboveexpression. Then, the change in the reconstructed wavelength is onlyabout 0.2 nm within the viewing angle range of ±2°, which is requiredfor a sign, whereby the change in color will not be recognized.Moreover, the color distribution within the reconstructed image can besuppressed to be extremely small. Since the reconstructed wavelengthslightly shifts toward the long wavelength side, the producing opticalsystem should preferably be set in view of such a shift.

FIG. 27A illustrates an installation of the hologram when theinstallation angle is set to be close to θac, and FIG. 27B illustrates anormal installation of the hologram for comparison.

When the installation angle of a hologram 53 is set to be as close toθac as possible, the optical path of illumination light 54 and that ofreconstructed light 55 come closer to each other. Thus, in practice, itis preferable to install the hologram while setting the installationangle to be as close to θac as possible and such that an observer 56attempting to view the reconstructed image does not block theillumination light 54. It is more preferable to slightly move a linearlight source for illumination, which is not shown, in the horizontaldirection so that the illumination light 54 and the observer 56 do notoverlap each other, as described in Embodiment 4.

The arrangement of the above-described embodiment as described above canbe practiced with an optical display apparatus of any of the embodimentsdescribed in this specification.

Embodiment 9

It is possible to increase the size of the virtual display plane andthat of the reconstructed image by increasing the size of the hologram.However, the exposure area which is normally realized by a hologramproducing optical system is about φ300 mm to about φ400 mm, whichpresents the limit for the size of the reconstructed image. Although itis not impossible to realize an exposure area larger than this, therewill then be problems as follows:

(1) The production of optical components such as a lens, a mirror, orthe like, is difficult and costly;

(2) The light intensity decreases as the laser beam is extremelywidened;

(3) The exposure time increases because of (2) above; and

(4) The exposure condition becomes unstable (increased probabilities foradverse effects such as air fluctuation, vibration, and laser stability)because of (3) above.

In order to avoid these difficult problems, with the optical displayapparatus of the present invention, a large-size hologram is provided byproviding small elementary holograms which can be produced under a morestable condition, and combining these elementary holograms together justlike tiling.

FIG. 28 illustrates an exemplary 1 m×1 m hologram. Herein, sixteen 25cm×25 cm elementary holograms are arranged in a 4×4 matrix, therebyrealizing the size of 1 m×1 m. Each elementary hologram is produced byusing one of elementary masks which are obtained by dividing a patternmask having a size of about 1 m×1 m, which is the object, into 4 equalparts. The problems as those described above do not occur in exposurefor the size of 25 cm.

The arrangement of the above-described embodiment as described above canbe practiced with an optical display apparatus of any of the embodimentsdescribed in this specification.

Embodiment 10

One feature of the optical display apparatus of the present inventionthat is not seen in conventional apparatuses is that the optical displayapparatus whose basic arrangement has been shown in each embodiment maybe used as one display unit, while a plurality of such units can bearranged on an arrangement plane so as to synthesize and displayreconstructed images from the respective units on the virtual displayplane. For example, where the display units are arranged side by side asviewed from the observer, the display width can be widened in thehorizontal direction by synthesizing the respective reconstructed imageson the virtual display plane.

FIGS. 29A and 29B are a front view and a side view, respectively, of anexemplary optical display apparatus in which three display units 57 arearranged side by side.

A hologram reconstructed image 59 reconstructed by a fluorescent lamp 58differs for the respective display units, and each display unitreconstructs and displays one of the characters “A”, “B” and “C”. Whenthe respective display units are closely arranged together side by side,as illustrated in the figure, the characters are aligned together sothat they can be recognized as one word.

It is preferable to arrange a shield plate 60 between the units so thatthe fluorescent lamp for one unit does not reconstruct the fluorescentlamp for another unit.

Embodiment 11

Where the information to be displayed is a string of characters as inFIG. 29A, even if there is a slight gap between the characters, theinformation is conveyed to the observer with no problem. However, wherethe information to be displayed is a pattern, any gap therein isundesirable, and in some cases the gap itself may be recognized as apiece of information, whereby the observer recognizes information whichis different from the original information intended to be conveyed. Inthe case of the arrangement of Embodiment 10, even when the hologramsfor the respective units are arranged together in a completelycontinuous manner, if the fluorescent lamps are arranged at the basicpositions, the reconstructed images from the respective holograms arereconstructed at separated positions on the virtual display plane,thereby causing the above-described problem.

In order to solve such a problem, the present embodiment employs themethod described in Embodiment 4 of the present invention. That is, theshift in the position where the reconstructed image is formed due to theoffset arrangement of the fluorescent lamps is positively utilized toprovide a large synthesized reconstructed image which is seamlessbetween the respective images.

FIGS. 30A and 30B are diagrams illustrating an exemplary optical displayapparatus in which three display units are arranged side by side fordisplaying a single large pattern, respectively showing separatedreconstructed images and reconstructed images which are seamlesslysynthesized together.

Each display unit is arranged to display an individual reconstructedimage as illustrated in FIG. 30A. When the units are arranged side byside, and a fluorescent lamp 62 of a left display unit 61 indicated by abroken line is moved to the left, a reconstructed image 63 is moved tothe right so that it is displayed adjacent to a reconstructed image 65of a center display unit 64 with no gap therebetween. Similarly, when afluorescent lamp 67 of a right display unit 66 is moved to the right, areconstructed image 68 moves to the left so that it is displayedadjacent to the reconstructed image 65 of the center display unit 64with no gap therebetween.

As described above, according to the present invention, it is possibleto combine reconstructed images together with no gap, thereby allowinglarge patterns to be displayed.

Embodiment 12

An arrangement which sufficiently exhibits the feature of the opticaldisplay apparatus of the present invention is one in which a pluralityof display units are arranged along a depth direction of thereconstructed image as viewed from the observer, so that thereconstructed images from the respective holograms are synthesized onthe virtual display plane.

FIG. 31A is a side view illustrating a structure of an optical displayapparatus according to Embodiment 12 of the present invention. In thisembodiment, the optical display apparatus of the present invention isused as a traffic sign in a tunnel. Specifically, reference numeral 69denotes an optical display apparatus of the present embodiment; 70 to 72display units; 73 to 75 holograms; and 76 to 78 fluorescent lamps aslinear light sources. The display units 70 to 72 are arranged side byside on a ceiling plane 80 of a tunnel 79.

An operation of the optical display apparatus 69 having such a structurewill be described below.

First, an original picture pattern 81 of a traffic sign indicating aspeed limit, as illustrated in FIG. 31B, is divided into parts andrecorded on the holograms 73, 74 and 75, respectively, by a method asthat described in Embodiment 1 of the present invention. In particular,as illustrated in FIG. 31C, an elementary pattern 82 for the lowerapproximately ⅓ portion obtained by dividing the original picturepattern 81, is recorded on the hologram 73, an elementary pattern 83 forthe middle approximately ⅓ portion is recorded on the hologram 74, andan elementary pattern 84 for the upper approximately ⅓ portion isrecorded on the hologram 75. Each hologram is produced by arranging apattern mask for the elementary pattern and a hologram dry plate at arespectively different distance in an optical system for producing eachhologram.

As illustrated in FIG. 31A, a reconstructed image 85 of the hologram 73formed by the fluorescent lamp 76 is arranged to be formed in thevicinity of a virtual display plane 86. Similarly, a reconstructed image87 of the hologram 74 formed by the fluorescent lamp 77 and areconstructed image 89 of the hologram 75 formed by the fluorescent lamp78 are arranged to be formed in the vicinity of a virtual display plane88 and a virtual display plane 90, respectively. Then, the reconstructedimages 85, 87 and 89 as viewed from the front side thereof aresynthesized into a single image, as illustrated in FIG. 31D. Thus, thereconstructed image is viewed from a car running through a tunnel 79 asif it were a traffic sign indicating a speed limit hung from a ceilingplane 80 of the tunnel 79. However, this is only a display on thevirtual display plane, and there is no object actually existing on thedisplay plane. Therefore, there is no chance for a car collision.

An advantage of this structure is that it is possible to reduce theheight of the display unit by a rate of approximately 1/N, where Ndenotes the number of display units provided. Thus, the cross sectionfor which a tunnel is to be dug through can be reduced by employing anoptical display apparatus having such an extremely flat structure. Thisprovides a substantial reduction in the construction cost.

Embodiment 13

FIG. 32 is a perspective view of an optical display apparatus accordingto the present embodiment. This is an example for displaying theposition of an emergency phone in a tunnel. Reference numeral 91 denotesa fluorescent lamp, 92 a hologram unit, and 93 an emergency phone.

The hologram unit 92 has a structure as illustrated in FIG. 33.Specifically, reference numeral 94 denotes a first hologram, 95 a secondhologram, and 96 a display board. The first hologram 94 and the secondhologram 95 are arranged to form a reconstructed image on the side of afirst plane 97 of the hologram unit 92 and on the side of a second plane98 of the hologram unit 92, respectively. Information identical todisplay information to be reconstructed by the first hologram 94 iswritten on a first plane 99 of the display board 96 to which the firsthologram 94 is attached. Similarly, information identical to displayinformation to be reconstructed by the second hologram 95 is written ona second plane 100 of the display board 96 to which the second hologram95 is attached.

The hologram unit 92 having such a structure is arranged under thefluorescent lamp 91 as a linear light source, as illustrated in FIG. 32.Referring to the side view of FIG. 34 in order to describe an operationof the hologram unit 92, a reconstructed image 103 of the first hologram94 is formed by illumination light 102 emitted from a region 101 of thefluorescent lamp 91. In this example, the characters “Emergency Phone”are displayed. On the other hand, a reconstructed image 106 of thesecond hologram 95 is formed by illumination light 105 emitted from aregion 104 of the fluorescent lamp 91, thereby similarly displaying thecharacters “Emergency Phone”. Therefore, it is possible to clearlyindicate the position of the emergency phone 93 to people on both sidesof the optical display apparatus. In this example, the characterinformation “Emergency Phone” is written on both sides of the displayboard 96, whereby a display on the opposite side can be recognizedthrough a transparent hologram plane. Therefore, even in an emergencywhere the fluorescent lamp 91 does not light up, for example, theposition of the emergency phone 93 can be recognized by using a flashlight.

While a case where identical information is displayed has been describedabove, it is understood that it is possible to display differentinformation on the opposite sides by recording different information onthe respective holograms.

Embodiment 14

FIG. 35 is a perspective view of an optical display apparatus accordingto the present embodiment. Reference numeral 107 denotes a fluorescentlamp, 108 a first hologram unit, and 109 a second hologram unit.

Each of the hologram units 108 and 109 has a structure as illustrated inFIG. 36. In particular, reference numeral 110 denotes a first hologram,111 a first display board, 112 a second hologram, and 113 a seconddisplay board. The first and second hologram units 108 and 109 arearranged near the respective ends of the fluorescent lamp 107 as alinear light source, as illustrated in FIG. 35.

An operation of the optical display apparatus according to the presentembodiment will be described with reference to FIG. 37.

A reconstructed image 115 of the first hologram 110 is formed byillumination light 114 emitted from the fluorescent lamp 107. On theother hand, a reconstructed image 117 of the second hologram 112 isformed by illumination light 116 emitted from the fluorescent lamp 107.Therefore, it is possible to display identical or different informationto people on both sides of the optical display apparatus.

Information identical to the reconstructed image 115 of the firsthologram 110 and information identical to reconstructed image 117 of thesecond hologram 112 are recorded on the first display board 111 and onthe second display board 113, respectively, and can be recognized fromthe opposite side through transparent hologram plane. Therefore, even inan emergency where the fluorescent lamp 107 does not light up, forexample, the information can be recognized by using a flash light.

In the structure described above, a display board is provided for anemergency display with one hologram being provided on each side of thedisplay board. In other applications, if a display board having such afunction is not necessary, the hologram unit may be replaced with asingle hologram. The hologram is a reflection-type hologram which isrecorded through double exposure from the front side and the reverseside thereof. Identical or different reconstructed images can beobserved from the respective sides of the hologram.

Embodiment 15

An example of an optical display apparatus where a plurality ofholograms are reconstructed from a single linear light source has beendescribed in Embodiments 13 and 14 above. The plurality of holograms tobe reconstructed do not have to be placed on the same installation planeas in the example described above.

FIG. 38 is a plan view of an optical display apparatus according to thepresent embodiment, where one hologram is arranged on a side wall andanother hologram is arranged on the ceiling.

Reference numeral 118 denotes a fluorescent lamp, 119 a first hologram,and 120 a second hologram. Illumination light 121 emitted from thefluorescent lamp 118 forms a reconstructed image 122 of the firsthologram 119, and illumination light 123 forms a reconstructed image 124of the second hologram 120. Such a reconstruction operation can berealized because the hologram of the present invention can bereconstructed by a fluorescent lamp.

The structure of an optical display apparatus for simultaneouslyreconstructing such a plurality of holograms is not limited to thisembodiment, but various other structures are possible by effectivelyutilizing light which is omnidirectionally emitted from the linear lightsource as illumination light.

While the reference light 16 is directed to be incident upon theincident plane 15 in a hologram producing process in Embodiment 1, thepresent invention is not limited to this. It may also be effective tointentionally not employ the arrangement. For example, when a hologramis formed by directing the object light to be incident upon the incidentplane while directing the reference light to be incident upon a planedifferent from the incident plane, the reconstructed image can be viewedfrom the front side of the hologram for illumination light coming fromthe left-hand side in the arrangement of the fluorescent lamp and thehologram illustrated in FIG. 38. Moreover, since the direction of thereflected light of the illumination light is different from thedirection in which the reconstructed image is obtained, an easy-to-viewdisplay is realized.

Embodiment 16

The method for producing a hologram of the present invention is notlimited to that described in Embodiment 1. For example, it is possibleto first reconstruct an image which has been recorded as atransmission-type hologram, and then to record it as a reflection-typehologram.

FIGS. 39A and 39B are a side view and a plan view, respectively, of anoptical system for producing a transmission-type hologram according tothe present embodiment.

As illustrated in FIG. 39A, laser light 126 incident upon a ground glass125 so as to be diffused light 127 and then incident upon a slit 128.The slit 128 has a narrow width as viewed from a side thereof, andtransmits only a portion of the diffused light 127. Therefore, lighthaving passed through the slit 128 appears as spread light coming from asingle point as viewed form the side. This light reads the informationof a pattern mask 129, and irradiates a hologram dry plate 130 as objectlight 131. This can be considered as projection of the pattern mask 129onto the hologram dry plate 130. The object light 131 including theinformation of the object forms interference fringes with referencelight 132 incident upon the same side of the hologram dry plate 130, andthe interference fringes are recorded on the hologram dry plate 130.

At this time, the “shadow” of the pattern mask 129 projected onto thehologram dry plate 130 has been enlarged. In view of the rate ofprojection magnification, the pattern mask 129 is produced while beingshrunk in one direction. Although the rate of magnification variesdepending upon the setting of the optical system, it normally is about1.2 to about 2.

As illustrated in the plan view of FIG. 39B, the slit 128 has a largewidth as viewed from the above, and transmits diffused light 127 comingfrom the ground glass 125 over a wide range. In FIG. 39B, diffused lighthaving passed through the central portion of the slit 128 is indicatedby a solid line, while diffused light having passed through an endportion of the slit 128 is indicated by a broken line. Information ofthe pattern mask 129 obtained when viewed from the front side thereof isprojected onto the hologram dry plate 130 by the diffused lightindicated by the solid line, whereas information of the pattern mask 129obtained when viewed from a slightly inclined direction through the endportion of the slit 128 is projected onto the hologram dry plate 130 bythe diffused light indicated by the broken line. The object light 131including such information forms interference fringes with the referencelight 132 incident upon the same side of the hologram dry plate 130, andthe interference fringes are recorded on the hologram dry plate 130.This is the principle of how reconstructed images of the pattern mask129 as viewed from different angles are formed on the respective eyes ofthe observer when the hologram is reconstructed.

Although side views and plan views have been separately described abovefor simplicity, it is understood that the interference fringes aresimultaneously recorded in an actual hologram producing process.

FIG. 40 illustrates an optical system for obtaining a reflection-typehologram from a master hologram, while using the hologram produced bythe above-described process as the master hologram. Illumination light134 which is directed to be incident upon a master hologram 133 is equalto the reference light 132 used when producing the master hologram. Theillumination light 134 forms reconstructed light 135 from the masterhologram 133. The reconstructed light 135 is incident upon a hologramdry plate 136 as object light and forms interference fringes withreference light 137 which is incident upon the reverse side thereof,thereby forming a reflection-type hologram.

As described above, in the present embodiment, a transmission-typehologram is once produced so as to produce a reflection-type hologramusing it as a master hologram. The method has an advantage that theoptical system for producing a reflection-type hologram can be arrangedeasily, and that the distance between the reconstruction display planeand the hologram can be re-adjusted. In particular, while areconstructed image 138 is formed at a position where the pattern mask129 was placed when producing the master hologram, the distance betweenthe master hologram 133 and the reconstructed image 138 is d1, whereasthe distance between the reflection-type hologram 136 and thereconstructed image 138 is d2. Thus, the amount by which thereconstructed image floats above the hologram plane can be increased ordecreased.

Embodiment 17

FIG. 41 illustrates an optical system for producing a hologram accordingto Embodiment 17. This is also a process of producing atransmission-type hologram once and then forming a reflection-typehologram while using it as a master hologram.

In FIG. 41, object light 141 obtained by irradiating an object 139,which is a three-dimensional object, with illumination light 140 formsinterference fringes with reference light 143 incident upon the sameside of a hologram dry plate 142. They are recorded on the hologram dryplate 142 as a transmission-type hologram, thereby providing a masterhologram 144.

In FIG. 42, a reconstructed image of the object 139 is obtained bydirecting illumination light 145, which is conjugate light of thereference light 143, to be incident upon the master hologram 144.Herein, a slit 146 is arranged in the vicinity of the master hologram144 so as to use light coming through the slit 146 as object light 147,so that interference fringes are formed between the object light 147 andreference light 149 incident upon the reverse side of a hologram dryplate 148. The interference fringes are recorded on the hologram dryplate 148 as a reflection-type hologram. Reference numeral 150 denotes areconstructed image of the object 139.

By employing such a method, it is possible to obtain an unblurredreconstructed image for a three-dimensional object or an object spacedapart from the hologram plane.

Embodiment 18

FIG. 43 illustrates an optical system for producing a hologram accordingto Embodiment 18. This is also a process of producing atransmission-type hologram once and then forming a reflection-typehologram while using it as a master hologram.

The optical system of FIG. 43 differs from that of FIG. 42 in that anegative cylindrical lens 151 and an opening 152 are provided in placeof the slit 146. By the action of the cylindrical lens 151, it ispossible to match the position in the vertical direction in the figurewhere reconstructed light 153 forms an image with a hologram dry plate154, whereby it is possible to obtain a sharp reconstructed image for athree-dimensional object or an object spaced apart from the hologramplane. Reference numeral 155 is a reconstructed image of object 139.

In FIG. 43, the cylindrical lens 151 having a negative power is used,assuming a case where the reconstructed image 155 is formed between themaster hologram and the hologram dry plate. However, when thereconstructed image 155 is formed on the left side of the hologram dryplate 154 in FIG. 43, a cylindrical lens having a positive power isused.

Embodiment 19

FIG. 44 is a side view illustrating a structure of an optical displayapparatus according to Embodiment 19 of the present invention. In thisembodiment, the optical display apparatus of the present invention isused as a traffic sign in a tunnel.

In FIG. 44, reference numeral 201 denotes an optical display apparatusof the present embodiment, 202 a hologram screen, 203 a cylindricallens, and 204 an LED display apparatus. The optical display apparatus201 is arranged on a ceiling plane 206 of a tunnel 205. As shown in thefigure, the width direction (perpendicular to the figure), thelongitudinal direction and the vertical direction of the tunnel 205 aredenoted as the x, y and z directions, respectively.

An image displayed on the LED display apparatus 204 is projected by thecylindrical lens 203 onto the hologram screen 202. The image diffractedand reflected by the hologram screen 202 is reconstructed and imaged ona virtual display plane 208. When an image 209 is viewed from a car inthe tunnel 205, it is seen as if a sign is hung at a position downwardlyspaced apart from a ceiling plane 206 of the tunnel 205. However, thisis only a display on the virtual display plane 208, and there is noobject actually existing on the display plane 208. Therefore, there isno chance for a car collision.

The virtual display plane 208 is a plane or a curved surface which isvirtually provided in a space. The light from reflected by the surfaceof the hologram screen 202 can be deflected in a direction toward theroad surface or in a direction toward the ceiling plane 206, whereby thereflected light will not be directly incident upon the driver's eye. Thereflected light is useful as illumination light for illuminating theroad surface or the ceiling plane.

A reason why the optical display apparatus of the present embodiment hassuch a function will be described below.

In FIG. 44, an image displayed on the LED display apparatus 204 isformed on the hologram screen 20Z by the cylindrical lens 203. The imagedisplayed on the LED display apparatus 204 is inverted in the verticaldirection and in the horizontal direction, and the generatrix of thecylindrical lens 203 is placed parallel to the x direction. Herein, therespective components are arranged so that only the z component of theimage is focused on the hologram screen 202. In other words, therespective components are arranged by the function of the cylindricallens 203 so that a line or outline contained in the image which extendsalong the x direction, for example, appears to be most clear on thehologram screen 202. As a result, when a normal projection screen isplaced at the position of the hologram screen 202, an image will beviewed where only the line or outline extending along the x direction isclear while the line or outline extending along the z direction isblurred, as illustrated in FIG. 45. FIG. 45 is a schematic illustrationshowing how a circular image and a square image imaged by thecylindrical lens 203 will appear on a normal projection screen beingplaced at the position of the hologram screen 202.

Next, a function of the hologram screen 202 will be described.

FIGS. 46A and 46B are a plan view and a side view, respectively,illustrating a structure with only the hologram screen 202 and the LEDdisplay apparatus 204 of the optical display apparatus 201. In theabsence of the cylindrical lens 203, the hologram screen 202 has afunction of imaging the light from point A on the LED display apparatus204 to point B on the virtual display plane 208.

The hologram screen 202 having such a function can be produced by, forexample, an exposure optical system illustrated in FIG. 47. Inparticular, a laser beam 211 focused by a lens 210 becomes diffusedlight after passing through a pin hole 212 placed at the position ofpoint A, and is incident upon a hologram dry plate 213, which will laterbe the hologram screen 202, from the right side of the figure. On theother hand, a laser beam 214 converging to point B is incident upon thehologram dry plate 213 from the left side of the figure, i.e., from theopposite side to the laser beam 211. The hologram screen 202 having sucha function is provided by recording an interference pattern of the twolaser beams on the hologram dry plate 213.

When the cylindrical lens 203 is arranged within the optical path, andan image is projected as illustrated in FIG. 45 in which only the zcomponent (i.e., the line or outline extending along the x direction) ofthe image is clear and the x component (i.e., the line or outlineextending along the z direction) is blurred, the hologram screen 202exhibits the following function.

FIGS. 48A and 48B are a plan view and a side view, respectively,illustrating how a light beam travels though the respective componentsof the optical display apparatus 201.

First, for the x component of the image, since it is not effected by thecylindrical lens 203, as illustrated in FIG. 48A, the image at point Adisplayed on the LED display apparatus 204 can be considered as beingprojected onto the hologram screen 202 as it is. Therefore, only the xcomponent (i.e., the line or outline extending along the z direction) issharply imaged on the virtual display plane 208 by the function of thehologram screen 202 as the light coming from point A being imaged atpoint B in FIG. 45.

The z component of the image, on the other hand, appears to be mostclear on the hologram screen 202 by the function of the cylindrical lens203 as described above. This is illustrated in FIG. 48B, where the imageat point A displayed on the LED display apparatus 204 is formed at pointC on the hologram screen 202. Light output from point A once spreads outin the z direction and passes through the cylindrical lens 203 so thatonly the z component thereof converges to point C with a certainconvergence angle. Therefore, after being diffracted and reflected bythe hologram screen 202, the light is projected onto the virtual displayplane 208 as divergent light having a small divergence angle along the zdirection.

Strictly speaking, the respective light beams contained in the divergentlight have slightly different wavelength components. That is, theemission distribution of the display apparatus has a width of severalten nm, and the light is split by the hologram screen 202 while beingdiffracted and reflected at different angles for the respectivewavelengths.

It has been described above how the image displayed on the LED displayapparatus 204 travels to be projected and imaged on the virtual displayplane 208 separately for the x component and the z component. Next, howthe image is consequently viewed by the eyes of an observer 215 will bedescribed.

FIGS. 49A and 49B are a plan view and a side view, respectively,illustrating only part of the light beams illustrated in FIGS. 48A and48B after the hologram screen 202, and illustrating the path of thelight beams to the pupils of the observer 215 who is viewing the imageat a position spaced apart from the virtual display plane 208.

As illustrated in FIG. 49A, similar light beams as those obtained whenlight comes from the single point B on the virtual display plane 208 areincident upon the left and right eyes of the observer 215. Thisindicates that the x component of the image appears to be a sharp lineor outline on the virtual display plane 208. The above-described imageis viewed by the observer 215 within the range indicated by two brokenlines.

As illustrated in FIG. 49B, similar light beams as those obtained whenlight comes from the single point C on the hologram screen 202 areincident upon the respective eyes of the observer 215. This indicatesthat the z component of the image appears to be a sharp line or outlineon the hologram screen 202. The above-described image is viewed by theobserver 215 within the range indicated by two broken lines.

It would appear that it would be difficult for human eyes to recognizethe x and z components as one image when they appear differently asdescribed above. However, in fact, it is not difficult.

A three-dimensional feeling or a depth feeling is perceived becausehuman eyes generally have a binocular parallax in the horizontaldirection. Herein, a binocular parallax refers to a phenomenon that theimage of a single object being viewed is projected onto differentpositions in the respective fields of view of the right eye and the lefteye, or to the positional difference. For example, assuming, forsimplicity, a case where a vertically extending long straight line isviewed by both eyes, both the right eye and the left eye can recognizeit as a vertically extending long straight line. At the same time,because the image is projected onto different positions in the eyes forthe respective eyes due to the binocular parallax, it is empiricallypossible to determine approximately how far the long straight line islocated in the horizontal direction.

For the vertical direction, on the other hand, such a binocular parallaxdoes not occur because the human eyes are located at the same height. Asa result, it is relatively difficult to perceive the three-dimensionalfeeling or the depth feeling. For example, assuming, for simplicity, acase where a laterally extending long straight line is viewed by botheyes, both the right eye and the left eye can recognize it as alaterally extending long straight line. However, no parallax occursbecause the image is projected onto the same position for both eyes.Therefore, it is not possible to definitely determine how far the longstraight line is located in the vertical direction. For example, thiscorresponds to a case where a person attempting to jump up to a highhorizontal bar might hesitate to jump for a moment because they cannotgrasp the distance to the horizontal bar which appears to extend in thehorizontal direction in the background sky.

Importantly, the binocular parallax in the horizontal direction is themost dominating factor for the three-dimensional feeling or the depthfeeling. Based on this, how the x and z components of theabove-described optical display apparatus of the present inventionappear will be discussed.

What is shown in FIG. 49A is the fact that the sharp line or outline ofthe x component of the image is viewed by each of the left and righteyes of the observer 215 on the virtual display plane 208. Using theabove figure of speech, this corresponds to how the vertically extendinglong straight line appears. Since the binocular parallax occurs for therespective left and right eyes of the observer 215, it is recognizedthat the image is located just on the virtual display plane 208.

On the other hand, what is shown in FIG. 49B is the fact that the sharpline or outline of the z component of the image is viewed by each of theleft and right eyes of the observer 215 on the hologram screen 202.Using the above figure of speech, this corresponds to how the laterallyextending long straight line appears. Since no binocular parallax occursfor the respective left and right eyes of the observer 215, the positionof the image cannot clearly be determined.

Therefore, the sharp line or outline of the x component is the primaryfactor for the binocular parallax, and is the dominating factor for therecognition of a position. As a result, the image appears to theobserver's eyes as if it were floating at the position of the virtualdisplay plane 208.

Although it has been omitted in the above description, the relativeinstallation angle among the hologram screen 202, the cylindrical lens203 and the LED display apparatus 204 is intentionally inclined. This isdone so that a matrix array of pixels, which are normally formed on theLED display apparatus 204 equidistantly in the vertical direction and inthe lateral direction, are clearly imaged on the hologram screen 202without being distorted. This is a technique called “front rising” whichis employed when photographing architecture. In particular, whenarchitecture such as a tall building is photographed by an ordinarycamera while looking up, it is photographed while the shape of thebuilding, which is originally rectangular, becomes a trapezoid asillustrated in FIG. 50. The front rising method is used for correctingsuch a distortion in the shape and taking a photograph with the entireobject being focused.

A procedure of the front rising method is illustrated in FIGS. 51A to51D. Herein, reference numeral 216 denotes a film surface, and 217 ashooting lens.

In particular, the camera is first directed from the normal position(FIG. 51A) toward the object (FIG. 51B), and then only the film surface216 is inclined in the direction parallel to the object (FIG. 51C).Then, the above-described distortion of the object is corrected. Next,the shooting lens 217 is inclined toward the direction parallel to theobject (FIG. 51D). Then, the entire object becomes focused.Incidentally, the nomenclature “front rising” comes from the fact thatthe shooting lens 217 is raised with respect to the film surface 216 asa result of the above-described procedure.

FIG. 52 is a diagram illustrating only the hologram screen 202, thecylindrical lens 203 and the LED display apparatus 204 of the opticaldisplay apparatus 201 of the present embodiment, with the elements beingrotated counterclockwise. It can be seen that, considering the LEDdisplay apparatus 204 as an object, the cylindrical lens 203 as ashooting lens, and the hologram screen 202 as a film surface, theoptical display apparatus 201 of the present embodiment has the samestructure as that of the above-described front rising technique.

What is described above is an arrangement of the optical displayapparatus 201 which is employed assuming that the LED display apparatus204 has a matrix arrangement of pixels which are provided equidistantlyin the vertical direction and in the lateral direction. However, thearrangement may vary in the case where it is possible to use a displayapparatus having a pixel arrangement for correcting a trapezoidaldistortion as illustrated in FIG. 50.

FIG. 53 is an arrangement employed when using a display apparatus 218which originally has a pixel arrangement of a vertically invertedtrapezoid for correcting the trapezoidal distortion.

The respective planes (indicated as straight lines in the figure) onwhich the hologram screen 202, the cylindrical lens 203 and the displayapparatus 218 are respectively arranged so that the extension linesthereof meet together at a single point. This is called a Scheimpflugcondition and is well known in the art of photography. When thiscondition is satisfied, the entire image displayed on the displayapparatus 218 is clearly projected onto the hologram screen 202.

According to the present invention, the color slightly varies among thelight beams in the z direction, but the change in color among thosereceived by a pupil is small, and thus they appear to have a singlecolor. In the above description of the method for producing the hologramscreen 202, only a method using a single color laser is described.However, it is possible to display a color image by performing multipleexposure with red, blue and green lasers using a similar method.

Moreover, while the cylindrical lens 203 is used in the presentembodiment, the present invention is not limited thereto. Any otherstructure may alternatively be used as long as it clearly projects andimages the z component of an image on the hologram screen 202 asdescribed above. For example, an anamorphic optical system havingdifferent focal distances for the vertical and lateral directions or acombination of a normal projection lens and a cylindrical lens may beused. Particularly, when using a lens or a mirror in which the focaldistance in the x direction can be varied, it is possible to easilychange the position along the depth direction where the image is viewed.For example, when a varifocal lens 301 having a power only in the xdirection is arranged as illustrated in FIGS. 54A and 54B, the positionof the virtual display plane 208 where the image is formed is moved backand forth without changing the position of the LED display apparatus204. It is also possible to employ an arrangement where the optical pathis folded by using a varifocal mirror in place of the varifocal lens301.

While an LED display apparatus is used as an image display apparatus inthe present embodiment, the present invention is not limited thereto butmay employ any image display apparatus capable of displaying a brightimage. For example, it is possible to use an image display apparatuscomprising: a display device selected from an LED, a CRT, a polymerdispersed type liquid crystal panel and an organic EL panel; and apolarization switching device. As the polarization switching device, anarrangement including a ferroelectric liquid crystal panel may be used.

As described above, with the optical display apparatus of the presentinvention, an image displayed on the LED display apparatus 204 isreconstructed and imaged on the virtual display plane 208. However, thisis only a display on the virtual display plane 208, and there is noobject actually existing on the virtual display plane 208. Therefore,there is no chance for a car collision. Moreover, since the height ofthe overall apparatus can be set to be low, it is possible to provide adisplay apparatus with which a small space can be efficiently utilized.

Moreover, while the optical display apparatus of the present inventionhas been primarily described with respect to an application for atraffic sign in a tunnel, the present invention is not limited thereto.Another optical display apparatus in a form similar to that describedabove in the present embodiment can easily be used as a projection typedisplay. Utilizing the characteristic that an image appears as if itwere floating apart from the screen surface toward the viewer, variousapplications may be possible in the field of games, amusement, etc.

In FIG. 47, the laser beam 214 converging to point B is directed to beincident upon the hologram dry plate 213 from the left side of thefigure when producing the hologram screen 202. However, it may bereplaced with a laser beam 219 which is divergent light coming frompoint E which is located on the left side of the hologram dry plate 213,as illustrated in FIG. 55. A hologram screen 220 produced in this manneris arranged as illustrated in FIG. 56. Since the elements except for thehologram screen 220 are not changed at all, the elements are arranged asdescribed above so that an image displayed on the LED display apparatus204 is projected and imaged by the cylindrical lens 203, whereby theline or outline contained in the image which extends along the xdirection, for example, is most clear on the hologram screen 220.

On the other hand, the x component of the image is not effected by thecylindrical lens 203. Therefore, it may be considered that the imagedisplayed on the LED display apparatus 204 is projected onto thehologram screen 220 as it is. Therefore, by the function of the hologramscreen 220, only the x component (i.e., the line or outline extendingalong the z direction) is sharply imaged on a virtual display plane 221,which is newly formed at the position where a point image E as a falseimage on the left side of the hologram screen 220 was located. Since aclear image of the x component is viewed by the observer on the virtualdisplay plane 221 beyond the hologram screen 220, an image is recognizedas if it were floating at this position as in the above description.

While such an optical display apparatus can be used as a traffic sign asin the above description, a more suitable field of application is ahead-up display. In the most commonly known application, it is arrangedon the dashboard of a car so as to display traffic information, speedinformation, navigation information, etc., which are required fordriving the car, beyond the windshield and above the bonnet. Anexemplary arrangement for use in such an application is illustrated inFIG. 57. In this case, other than an LED display apparatus, a CRT, aliquid crystal display apparatus, a fluorescent display tube, an organicEL, and the like, may be used as the display apparatus 204. Moreover,the hologram screen 220 is produced through an interference of divergentlight as in the case of producing the hologram screen 220 describedabove. The hologram screen 220 may be provided on the windshield.Moreover, the projection optical system may be a cylindrical lens, ananamorphic optical system, or a combination of a normal projection lensand a cylindrical lens, as described above.

Embodiment 20

According to the present invention, it is possible to project atwo-dimensional image at a position spaced apart from the screen. Byapplying the principle, it is also possible to provide a displayapparatus for providing a three-dimensional image. This will bedescribed in detail below.

When a person views a three-dimensional object, an image of the objectviewed by the right eye and that viewed by the left eye are slightlydifferent from each other. Based on this subtle difference called abinocular parallax, the person recognizes the three-dimensionalstructure and the depth of the object. Many three-dimensional displayapparatuses have been proposed in the art which utilize this principle,where the display apparatus is controlled to alternately display aright-eye image and a left-eye image, thereby independently showing theright eye and the left eye the respective images, so that athree-dimensional image is recognized.

Generally, when viewing a three-dimensional image, a person is likely toget a tired feeling and, in some cases, may even feel sick as when aperson has car sickness. Such a physiological phenomenon, though itdepends on individuals, has been found to be a problem associated with athree-dimensional image. There has been a research and development forsolving the problem.

By applying the above-described three-dimensional image displayprinciple to the display apparatus of the present invention, it ispossible to provide a new three-dimensional display apparatus whichsolves such problems. The arrangement is schematically shown in FIG. 58.Specifically, reference numeral 420 denotes a hologram screen, 402 aspatial light modulation device, and 403 a projection optical system. Athree-dimensional image 406 is observed by an observer 415 wearingpolarization glasses 404.

Herein, the spatial light modulation device 402 may be any image displayapparatus capable of switching the polarization direction of thedisplayed image, and may be those capable of switching the direction oflinearly-polarized light, those capable of switching the rotarydirection of circularly-polarized light, or the like. As the spatiallight modulation device 402, those operating at 120 Hz or more arecommonly available, with which a three-dimensional image can bedisplayed based on the binocular parallax by switching images from oneto another at a speed such that the switching cannot be recognized byhuman eyes. The spatial light modulation device 402 may alternatively beprovided by using such a device as the polarization switching device incombination with a non-polarization type display device, e.g., a CRT, anorganic EL, a polymer dispersed type liquid crystal panel, etc.

Moreover, as the simplest arrangement for the projection optical system403, a cylindrical lens may be used as already described above. However,the projection optical system 403 is not limited thereto, but may be anysystem which clearly projects and images the z component of the image onthe hologram screen 420. For example, an anamorphic optical systemhaving different focal distances for the vertical and lateral directionsor a combination of a normal projection lens and a cylindrical lens maybe used. As described above, when using a lens or a mirror in which thefocal distance in the x direction can be varied, it is possible toeasily change the position along the depth direction where the image isviewed. For example, when a varifocal lens having a power only in the xdirection is arranged as illustrated in FIGS. 54A and 54B, the positionof the virtual display plane where the image is formed is moved back andforth without changing the position of the LED display apparatus. It isalso possible to employ an arrangement where the optical path is foldedby using a varifocal mirror in place of the varifocal lens.

The respective orientations of the polarizing plates of the polarizationglasses 404 are arranged to be orthogonal to each other, so that images,which are switched from one to another by the above-described spatiallight modulation device 402, can be independently recognized by theright eye and the left eye by wearing the polarization glasses 404.

A feature of the three-dimensional display apparatus of the presentinvention is that the screen surface and the position where the image isobserved can be separated from each other, while the distancetherebetween can be varied. This is what makes it possible to solve theabove-described problems such as the tired feeling. In particular, sincethe image is not fixed on the screen surface, the focus of the eye isadjusted to the actual image, but not to the screen. Moreover, since theposition of the image can be changed, it is possible to adjust the focusof the eye and the angle of convergence to where the actual image isbeing viewed, thereby allowing for a natural three-dimensional display.

Embodiment 21

As described above, one feature of the optical display apparatus of thepresent invention that is not seen in conventional apparatuses is thatthe optical display apparatus whose basic arrangement has been shown ineach embodiment may be used as one display unit, while a plurality ofsuch units can be arranged on an arrangement plane so as to synthesizeand display reconstructed images from the respective units on thevirtual display plane.

FIGS. 59A and 59B are a side view and a front view, respectively, of anexemplary optical display apparatus in which three display units 233 arearranged side by side.

An image 225 formed on a virtual display plane 224 differs for therespective display units, and in the illustrated example, each displayunit reconstructs and displays one of the characters “A”, “B” and “C”.When the respective display units are closely arranged together side byside, as illustrated in the figure, the characters are aligned togetherso that they can be recognized as one word.

Alternatively, as illustrated in FIG. 60, a single large pattern may bedisplayed while being divided into three patterns 270, 271 and 272,which are synthesized together on the virtual display plane.

Thus, in the case where the display units are arranged side by side asviewed from the observer, the display width can be widened in thehorizontal direction by synthesizing the respective reconstructed imageson the virtual display plane.

Moreover, an arrangement which sufficiently exhibits the feature of theoptical display apparatus of the present invention is one in which aplurality of display units are arranged along a depth direction of theimage as viewed from the observer, so that the images from therespective display units are synthesized on the virtual display plane.

FIG. 61 is a side view illustrating a structure of an optical displayapparatus 226 in which a plurality of display units are arranged in adepth direction of an image. In this embodiment, the optical displayapparatus 226 of the present invention is used as a traffic sign in atunnel. Specifically, in FIG. 61, reference numeral 226 denotes anoptical display apparatus of the present embodiment, and 227 to 229display units, and the display units 227 to 229 are aligned with oneanother on a ceiling plane 231 of a tunnel 230.

A hologram screen of each of the display units 227 to 229 is produced bythe producing optical system illustrated in FIGS. 62A to 62C. Each ofthese optical systems is basically the same as that illustrated in FIG.47. However, they differ from one another on the point at which anincident laser beam as convergent light is focused.

FIG. 62A illustrates an optical system for producing a hologram screenused in the display unit 227, and a laser beam 232 is incident so as toconverge to point F. FIG. 62B illustrates an optical system forproducing a hologram screen used in the display unit 228, and a laserbeam 233 is incident so as to converge to point G. FIG. 62C illustratesan optical system for producing a hologram screen used in the displayunit 229, and a laser beam 234 is incident so as to converge to point H.

As illustrated in FIG. 61, an image 235 of the display unit 227 isformed in the vicinity of a virtual display plane 236. Similarly, animage 237 of the display unit 228 and an image 239 of the display unit229 are formed in the vicinity of a virtual display plane 238 and avirtual display plane 240, respectively.

Elementary patterns 242, 243 and 244, as illustrated in FIG. 63B, whichare obtained by dividing an original picture pattern 241 of a trafficsign indicating a speed limit, as illustrated in FIG. 63A, are displayedon the display units 227, 228 and 229, respectively. In particular, anelementary pattern 242 for the lower approximately ⅓ portion obtained bydividing the original picture pattern 241 is displayed as the image 235on the display unit 227. Similarly, an elementary pattern 243 for themiddle approximately ⅓ portion is displayed as the pattern 244 for theupper approximately ⅓ portion is displayed as the image 239 on thedisplay unit 229.

Then, the reconstructed image 235, 237 and 239 as viewed from the frontside thereof are synthesized into a single image, as illustrated in FIG.63C, which is viewed from a car running through the tunnel 230 as if itwere a traffic sign indicating a speed limit hung from the ceiling plane231 of the tunnel 230. However, this is only a display on the virtualdisplay plane, and there is no object actually existing on the displayplane. Therefore, there is no chance for a car collision.

An advantage of this structure is that it is possible to reduce theheight of the display unit by a rate of approximately 1/N, where Ndenotes the number of display units provided. Thus, the cross sectionfor which a tunnel is to be dug through can be reduced by employing anoptical display apparatus having such an extremely flat structure. Thisprovides a substantial reduction in the construction cost.

As described above, the optical display apparatus using the hologram ofthe present invention has an extremely high industrial value because itallows, for the first time, one to use a light source such as afluorescent lamp which is inexpensive and has a long life.

However, the light source for utilizing the feature of the opticaldisplay apparatus of the present invention is not limited to afluorescent lamp, but may be any elongated linear light source. Inaddition to the combination of a lamp with a vertically elongatedopening, and the straight tube fluorescent lamp, as described above, aone-dimensional array of small electric bulbs, a one-dimensional arrayof semiconductor lasers or LEDs, an organic EL in which the lightemitting section is linearly shaped, a light source including a linearoptical output section which is provided by guiding light from a lightsource by using light guiding means such as an optical fiber, and thelike, can easily be used as the linear light source. Furthermore,various alternatives can be used. For example, it is possible to providea pseudo-linear light source by combining a point light source with acylindrical mirror or with a polygon mirror. It is also preferable touse a decentered mirror to reduce the size. Alternatively, it ispossible to form a linear light source by using light beams which arelinearly focused by a mirror or a lens. With this structure, it ispossible to provide a virtual linear light source having a highbrightness at a position near the hologram. Alternatively, it ispossible to allow a two-dimensional display apparatus such as a CRT tofunction as a linear light source by displaying a vertical elongatedbright line thereon. If the position where the bright line is displayedis successively moved, the reconstruction position also moves inresponse thereto, whereby it is possible to produce an effect that thereconstructed image is viewed as moving. Other than this, similareffects can be provided by using a movable linear light source.

Regarding the emission characteristics of the light source, the lightsource to be used may have a continuous emission distribution orindependent emission peaks corresponding to the three primary colors.Alternatively, a linear light source may be provided by combiningindependent light sources corresponding to the three primary colors. Inthis way, it is possible to turn on/off the light sources of therespective colors, thereby allowing for an extremely effective displaywhere a reconstructed image of a particular color is displayed or notdisplayed.

In FIG. 8, when the hologram 2 is reversed by 180° about an axisorthogonal to the figure plane, the virtual display plane on which thereconstructed image is formed is moved to the other side of the hologram2, i.e., to the other side of the ceiling plane 7 in FIG. 8, whereby thereconstructed image is formed on the other side of the hologram 2. Theoptical display apparatus of the present invention can produce such adisplay of a reconstructed image. However, in such a case, the obtainedreconstructed image is reversed. Therefore, when displaying areconstructed image with such an arrangement, it is necessary topreviously set the pattern mask so as to face toward the hologram dryplate when producing the hologram 2.

When the reference light is formed by directing a plurality of beams tooverlap with one another in the direction orthogonal to the longitudinaldirection of the slit, it is possible to widen the viewing range withoutusing a linear light source during the reconstruction. In such a case,the illumination light source may be a point light source. However,positions where the reconstructed image is observed are inherentlydiscrete. Therefore, as the view point is moved in the verticaldirection, a position where the reconstructed image can be viewed and aposition where it is difficult to view the reconstructed image willalternately occur. This condition varies depending upon how much theplurality of beams used when producing the hologram overlap with oneanother. In the case where the plurality of beams are arranged to beadjacent to one another, the reconstructed image is observed withoutinterruption even when the view point is moved. This reference lightarrangement is effective not only when the object light is formed bycombining a slit and diffused light, but also when a cylindrical lens isfurther combined therewith, when a reconstructed image of atransmission-type hologram is used as object light, or when the objectlight is provided by diffused light diffusing in one direction.

Alternatively, the viewing range can be widened by exposing the hologramwhile arranging a one-dimensional diffuser such as a lenticular lenssheet to be adjacent to the hologram dry plate, without using a linearlight source during the reconstruction. In such a case, the illuminationlight source may be a point light source. However, positions where thereconstructed image is observed are inherently discrete. Therefore, asthe view point is moved in the vertical direction, a position where thereconstructed image can be viewed and a position where it is difficultto view the reconstructed image will alternately occur. This conditionvaries depending upon the specification of the lenticular lens sheet. Byselecting a lenticular lens sheet having a fine pitch, the reconstructedimage is observed without interruption even when the view point ismoved.

The reconstruction display plane is not limited to a single plane, butmay be formed by a plurality of planes or a curved surface. Moreover, asalready described in some of the embodiments above, a three-dimensionalobject may be used as the object. However, when a three-dimensionalobject is used as the object with the hologram producing optical systemillustrated in FIGS. 10, 11A and 11B, it is necessary to rearrange theoptical system so that the reflected light from the object, which isgenerated by irradiating the three-dimensional object with laser light,passes through a slit placed between the object and the hologram dryplate. Also in such a case, while the light having passed through a slitbecomes the object light, the laser light and the object light will notbe aligned with the optical axis.

A duplicate of the hologram 2 can easily be produced. For example, theinformation recorded on the hologram 2 can be transferred and duplicatedonto a hologram dry plate by closely attaching together the hologram 2and an unexposed hologram dry plate, preferably via a refractive indexmatching solution, and by directing laser light to be incident thereuponfrom the hologram dry plate side at an appropriate angle.

In the above-described embodiments, an optical traffic sign and atraffic information display board have been mainly described asapplications of the present invention. However, the present invention isnot at all limited to such applications, but may also display generalcharacter information, advertising bill, etc. Similarly, the locationwhere the hologram is installed is not limited to the inside of atunnel, but a significant effect is also provided when it is installedin a building, an elevator, an underground town, a train station, or thelike. Moreover, it is also possible to employ an arrangement such thatnon-diffracted light which is not diffracted by the hologram is used forambient illumination.

Furthermore, the position where the hologram is installed is not limitedto the ceiling, but it is also effective to install the hologram on awall surface, a floor, or the like. For example, by installing ahologram on a floor surface of a hall so that it is reconstructed by afluorescent lamp for illumination which has been provided on the ceilingso as to display as a reconstructed image an indication indicating anarrow, a position, etc., the hologram functions as a guide sign.Particularly, it can easily be viewed when it is arranged so that thereconstructed image is displayed while floating apart from the floorsurface by several ten cm. Alternatively, such a display may be used asmeans to stop a passer-by since it attracts people's attention.

Embodiment 22

With the optical display apparatus using a hologram based on theprinciple of the present invention, it is possible to present a space tothe observer by displaying an indication indicating an arrow or alocation as a reconstructed image. As an exemplary application of thisfeature, a system for visualizing and presenting to a user a positionthrough which a non-contact type card is to be passed will be describedin the present embodiment.

In the case of a railroad station, for example, automatic ticket gatesystems currently installed are mainly those of the type whichmagnetically reads information recorded on a pass. However, it has beenproposed to replace them in the future with those of a type which readsinformation of a pass carried by a user by means of an electric wave, orthe like, in a non-contact manner. This aims to replace the existingticketing system, where the pass is supposed to be inserted into amachine, to improve the ticketing efficiency and realize a smoother flowof people by allowing a user to pass through the gate while holding anon-contact type card pass in its hand.

A point about which to be concerned is whether the user can effectivelypass the pass through a predetermined communication area (e.g., an areawhere a signal is read by a radio wave) which is prescribed in a spacespaced apart from a card reader. If the user cannot accomplish this welland thus has to repeat the reading operation, it will rather stagnatethe flow of people through the ticket gate.

The problem of effectively passing a card through the communication areais inherent to the non-contact type card system because, with aconventional reader, the user is only required to insert the card intothe slot, and the positioning of the card for the reading operation isautomatically done by the machine. Therefore, the user bears no burdenfor the card to be properly read. With the non-contact type card system,on the other hand, the communication area is spatially spread out, andit is an essential condition to bring the card into the optimalcommunication area and to keep the card presented within thecommunication area for a period of time which is required for readingthe information thereon. The user is responsible for all of such tasks.

In order to reliably read the card without imposing a burden on the userunder such circumstances, it is considered as an effective measure tovisualize a position (area) through which the non-contact type cardshould be passed. With the optical display apparatus of the presentinvention, it is possible to display an indication such as an arrow inthe form of a clear color image obtained by reconstructing a hologram ina communication area which is spaced apart from the card reader, wherebyit is possible to reliably present a position where the card should beput for the user passing by the position.

Moreover, users passing through a ticket gate are generally in a hurry.Therefore, a display where the communication area is seen only when theuser is passing by the area does not provide the intended function. Thisis because the action of moving the card to the optimal position afterthe display is seen imposes a burden on the user. Thus, in order toreliably inform the user of the position of the communication area, thedisplay should be such that the user can generally grasp the position ofthe communication area as the user approaches the ticket machine. Theoptical display apparatus of the present invention effectively functionsfor this purpose.

For example, as described above in connection with Embodiment 3, withthe optical display apparatus of the present invention, the displayviewing range can be widened back and forth by adjusting the arrangementof the light source. By using this function, it is possible to create asituation where the user sees something when the user is still away fromthe ticket gate. Therefore, the user can prepare to present the cardunder the guidance of what is seen. As the user approaches the ticketgate, the display starts to appear clearer, whereby the user cancertainly see where to put the pass. When the user actually passes theticket gate, the user can pass by while holding the card at anappropriate height and position, thereby allowing for a reliableinformation reading operation.

The above-described “situation where the user sees something” may beprovided by any display which attracts a person's attention, e.g., asthe user walks toward the presented position, the position appearsblinking or appears to change in color. The feature of the presentinvention, i.e., a hologram produced by a plurality of reference lightbeams alternately appears and disappears as the viewing positionchanges, can be effectively used for this purpose. Alternatively, thiscan be realized by providing the optical display apparatus whileavoiding an arrangement in which the change in color is small.

Regarding the viewing range, it is preferable that the range is set tobe wide in the front side while the range is such that the presentedposition can still be seen when the user looks back after passing by theposition. This can also be realized by defining the display viewingrange by adjusting the arrangement of the light source as describedabove in connection with Embodiment 3.

Since the user's height differs between individuals, the positionpreferably appears bright even when the viewing height changes. This canbe realized by increasing the degree of diffusion of the diffuser usedwhen producing the hologram while elongating the slit, or by increasingthe width of the one-dimensional diffuser and the degree of diffusionthereof.

Incidentally, Japanese Laid-Open Publication No. 9-6935 relating to awireless card processing apparatus describes that a three-dimensionalstereoscopic image is displayed by a hologram projection apparatus inwhich an area substantially equal to the communication area is hatched.However, use of the method proposed by the present invention isessential to actually realize such a function.

While a non-contact type card system is described above as an example,the optical display apparatus of the present invention can also becombined with other information communication apparatuses, e.g., a POSsystem. In such a case, an optical display system to be provided has anoptical display apparatus which three-dimensionally displays thecommunication area of the information communication apparatus.Preferably, the display area of the optical display apparatus and thecommunication area of the information communication apparatus arematched with each other. The information communication apparatus mayhave an arrangement for communicating information in one way (eitherreception or transmission) or an arrangement for performing a two-wayinteractive communication (reception and transmission).

Industrial Applicability

With the above-described arrangement, the present invention displays areconstructed hologram image, whereby an insubstantial hologramreconstructed image can be displayed on an insubstantial plane which isvirtually provided in a space. Moreover, the display apparatus itself isarranged in a flat area which is extremely close to the wall surface ofthe installation site, and thus has a small protruding portion, therebyeliminating the problems associated with the conventional displayapparatus such as an increase in the size of the display apparatus, anincrease in the installation area (occupied area), or an accidentalcollision with the display apparatus.

Moreover, according to the present invention, it is possible to use afluorescent lamp as a reconstruction light source, whereby thereconstructed light source is available anytime and anywhere. Thus, byproducing a hologram on a light-weight flexible substrate, it ispossible to realize a display apparatus which can easily be carriedaround.

Furthermore, by applying this principle, a novel display, such as ahead-up display or a three-dimensional display apparatus, is realized inwhich an image is observed at a position spaced apart from the screensurface.

For example, when the optical display apparatus of the present inventionis used in a non-contact type card system, a spatially spreadcommunication area can be clearly presented to the user, whereby it ispossible to more reliably and effectively provide the function inherentto the non-contact type card system.

What is claimed is:
 1. An optical display apparatus, comprising a hologram device and a light source, wherein the hologram device is a reflection-type hologram formed by: light having information of an object incident on a first side of a first hologram dry plate; and reference light incident on a second side of the first hologram dry plate, the second side of the first hologram dry plate being opposite the first side of the first hologram dry plate, the reference light and the light having the information of the object being arranged to interfere with each other on the first hologram dry plate, wherein a reconstructed image of the object is displayed by light from the light source which is incident on the reflection-type hologram through an elongated opening which is elongated in the length or depth direction with respect to a viewer but not substantially elongated in the width direction with respect to a viewer, such that the visible zone of the reflection-type hologram is lengthened without blurring, and wherein the light having the information of the object is obtained by reconstructing a transmission-type hologram which is formed by: object light incident on a second hologram dry plate, said object light obtained by irradiating the object which is positioned between a slit and the second hologram dry plate; and interfering with a second radiation light incident on the second hologram dry plate with an incident optical path different from that of the object light.
 2. An optical display apparatus according to claim 1, wherein diffused light is formed by passing light through a ground glass.
 3. An optical display apparatus, comprising a hologram device and a light source, wherein the hologram device is a reflection-type hologram formed by: light having information of an object incident on a first side of a first hologram dry plate; and reference light incident on a second side of the first hologram dry plate, the second side of the first hologram dry plate being opposite the first side of the first hologram dry plate, the reference light and the light having the information of the object being arranged to interfere with each other on the first hologram dry plate, wherein a reconstructed image of the object is displayed by light from the light source which is incident on the reflection-type hologram through an elongated opening which is elongated in the length or depth direction with respect to a viewer but not substantially elongated in the width direction with respect to a viewer, such that the visible zone of the reflection-type hologram is lengthened without blurring, and wherein the light having the information of the object is obtained by reconstructing a transmission-type hologram through a slit adjacent to the transmission-type hologram on which an image of the object is recorded.
 4. An optical display apparatus, comprising a hologram device and a light source, wherein the hologram device is a reflection-type hologram formed by: light having information of an object incident on a first side of a first hologram dry plate; and reference light incident on a second side of the first hologram dry plate, the second side of the first hologram dry plate being opposite the first side of the first hologram dry plate, the reference light and the light having the information of the object being arranged to intercept with each other on the first hologram dry plate, wherein a reconstructed image of the object is displayed by light from the light source which is incident on the reflection-type hologram through an elongated opening which is elongated in the length or depth direction with respect to a viewer but not substantially elongated in the width direction with respect to a viewer, such that the visible zone of the reflection-type hologram is lengthened without blurring, and wherein the light having the information of the object is obtained by reconstructing a transmission-type hologram through a slit having an aperture adjacent to the transmission-type hologram on which an image of the object is recorded; and a cylindrical lens having its generatrix along a longitudinal direction of the aperture of the slit.
 5. An optical display apparatus, comprising a hologram device and a light source, wherein the hologram device is a reflection-type hologram formed by: light having information of an object incident on a first side of a first hologram dry plate; and reference light incident on a second side of the first hologram dry plate, the second side of the first hologram dry plate being opposite the first side of the first hologram dry plate, the reference light and the light having the information of the object being arranged to interfere with each other on the first hologram dry plate, and wherein a reconstructed image of the object is displayed by light from the light source which is incident on the reflection-type hologram through an elongated opening which is elongated in the length or depth direction with respect to a viewer but not substantially elongated in the width direction with respect to a viewer, such that the visible zone of the reflection-type hologram is lengthened without blurring.
 6. An optical display apparatus according to claim 5, wherein the light having the information of the object is reconstructed light obtained by reconstructing a transmission-type hologram which is formed by: object light obtained by irradiating the object with diffused light; and irradiation light having an incident optical path different from that of the object light.
 7. An optical display apparatus according to claim 6, wherein the reference light is provided by superposing a plurality of beams on one another in a direction orthogonal to the direction in which the diffused light diffuses.
 8. An optical display apparatus according to claim 5, wherein the light having the information of the object is obtained by reconstructing a transmission-type hologram through a slit adjacent to the transmission-type hologram on which an image of the object is recorded.
 9. An optical display apparatus according to claim 8, wherein the reference light is provided by superposing a plurality of beams on one another in a direction orthogonal to a longitudinal direction of the slit.
 10. An optical display apparatus according to claim 5, wherein the light source is a linear light source.
 11. An optical display system having a plurality of display units arranged on an arrangement plane in which reconstructed images from the plurality of units are synthesized and displayed, wherein each of the plurality of units is an optical display apparatus according to claim
 5. 12. An optical display apparatus according to claim 5, wherein the hologram device is formed on a flexible substrate.
 13. An optical display apparatus according to claim 5, wherein the hologram device is portable.
 14. An optical display apparatus according to claim 5, wherein: the light source is a linear light source; and a length and an installation direction of the linear light source are set so that a predetermined reconstructed image viewing range is obtained.
 15. An optical display apparatus according to claim 5, wherein: the light source is a linear light source; and the linear light source is installed out of an incident plane.
 16. An optical display apparatus according to claim 5, comprising a plurality of the hologram devices, wherein the plurality of hologram devices are reconstructed by one light source, and respective reconstructed images are synthesized together on a space which is spaced apart from the plurality of hologram devices so as to obtain a desired reconstructed image.
 17. An optical display apparatus according to claim 5, wherein: the light source is a linear light source; and the linear light source is a fluorescent lamp or a combination of a fluorescent lamp and a reflecting plate.
 18. An optical display apparatus according to claim 5, wherein the light source is a linear light source comprising a polygon mirror and a point light source.
 19. An optical display apparatus according to claim 5, wherein the light source is a linear light source comprising a cylindrical mirror and a point light source.
 20. An optical display apparatus according to claim 5, wherein the light source is a linear light source configured by a light beam which is linearly focused by a mirror or a lens.
 21. An optical display apparatus according to claim 5, wherein the light source is a linear light source comprising an array of a point light sources.
 22. An optical display apparatus according to claim 5, wherein the light source is a linear light source configured by a bright line displayed on a two-dimensional display apparatus.
 23. An optical display system, comprising an optical display apparatus and an information communication apparatus, wherein the optical display apparatus is an optical display apparatus according to claim
 5. 24. An optical display system according to claim 23, wherein the optical display apparatus three-dimensionally displays a communication area of the information communication apparatus.
 25. An optical display system according to claim 24, wherein a display area of the optical display apparatus and the communication area of the information communication apparatus match with each other.
 26. An optical display system according to claim 23, wherein the information communication apparatus performs a one-way communication or an interactive communication of information. 